Sociometry in the narrow sense that has been developed by Moreno, Jennings and their collaborators for the purpose of measuring and analysing the phenomena of human relations is considered to have two approaches. One is that which takes up a group as a whole and emphasizes the description and analysis of group structure and developmental processes. The other is that which takes up the individual as a group member and attempts to show how his personality is projected in the choice process, his status in the group, etc. The present investigation has tried to clarify the effects of school class reorganization on friendship patterns among class-mates and their status, by means of a spciometric test, in view of both the above-mentioned two approaches. For this investigation, three sociometric tests were administered to high school boys and girls during the period from the third term of the first year to the third term of the second year. The first test was given at the end of the third term of the first year, the second in the middle of the first term of the second year, the third at the end of the third term of the second year. Classes were reorganized when the high school pupils were promoted from the first year to the second year. For the criteria of choice in this sociometric test, three situations were selected, namely "to play with", "to study with" and "to have as best friend", which were considered to be the most significant in high school life. The subjects were free to choose without limitation. The degrees of intensity of choice were shown in such a manner as to combine the special choice, " I like (or dislike) him epsecially " and the answer to the question, "By whom will you be chosen with the mere choice, "I like (or dislike) him". The following results were obtained from the investigation based on the foregoing plan. I. Effects of reorganization of school classes on friendship patterns among class-mates. (1) For every criterion, friendly relations were established earlier than hostile relations in the new classes, after the reorganization of classes. (2) The reorganization of classes at the turn of the school year expanded the range of pupils' acquaintance and resulted in the formation of large numbers of friendly relations over a wide range and at the same time, of small numbers of hostile relations. (3) When the second test was conducted immediately after the reorganization, mutual relations appeared to decrease ignificantly in number, and the rate of the strong ones to all the mutual relations became very low. This tendency was marked especially in the case of the criterion of "to have as best friend". (4) Mutual relations began to increase in number again for every criterion after the reorganization, and many more mutual relations were established at the time of the third test than at the time of the first test just before the reorganization. This tendency for increase of mutual relations was more marked in the case of stronger mutual relations. (5) Mutual relations immediately after the reorganization tended to be established comparatively easily among pupils who had been in the same class in the previous school year. This tendency appeared markedly for stronger mutual relations and also for the criterion of "to have as best friend". (6) For the criterion of "to play with", the above-mentioned tendency declined gradually with formation of mutual awareness among pupils in the new classes. Also, many mutual relations were formed among pupils who were in different classes in the previous school year. For the criterion of "to have as best friend", no such declining tendency was found. (7) When pupils who had formed mutual relations at some intensity or other in the former class were put into the same new class again, it was found that the stronger their relations in the former class, the more they were preserved in the new class; the weaker their previous relations, the more strongly they were influenced by the reorganization and the more they were dissolved in the new class. This tendency was marked especially for the criterion of "to have as best friend. (8) When pupils who had formed mutual relations at some intensity or other in the older class were scattered into the different new classes, almost of their mutual relations were dissolved except the strong ones. Furthermore, even such strong mutual relations declined gradually with the passing of time and almost of them also were dissolved at the time of the third test with the exception of the extremely strong ones. The strong mutual relations which had been formed for the criterion of "to have as best friend", however, kept the relations as they had been. (9) For both criteria of "to play with" and "to have as best friend", the mutual relations showed changes even with the mere passing of time without such a violent change of circumstances as the class reorganization. However, the changesin this case were more slight than in the case that the reorganization was introduced (10) Even when the mutual relations showed changes merely with the passing of time, it was found that the stronger the relations, the more stable they were and the less they were liable to change; the weaker the relations, the more unstable they were and the more they were liable to change. I. Effects of reorganization of school classes on pupils' status. (1) Analysis of the changes in pupils' status was made only for the criterion of "to play with". (2) Throughout the three tests about two-thirds of the pupils experienced changes in status in some way or other. (3) For more than half of them, status immediately after the reorganization of classes (or at the time of the second test) was only tentative and was transformed gradually to a stable condition with the formation of mutual awareness among them. (4) Subsequently, many of them returned to the status which they had occupied before the reorganization of classes. (5) However, a rough classification of their status was achieved almost immediately after the reorganization of classes. Thereafter, few of them exhibited extreme mobility (e.g., from "star area" to "low status area" or vice versa). (6) The pupils who received either the highest or the lowest status in the new classes occupied their fixed status earlier than the others after the reorganization. (7) Changes in status due to reorganization appeared to occur more often with pupils in the middle status than with ones in the high or low status positions in the original classes. (8) Even when the reorganization had taken place, few of them changed their status radically from "star area" to "low status area" or vice versa. (9) "Stars" seemed to be of two kinds: the "stable stars" who always kept their high status and the "unstable stars" who were liable to shift in status due to slight changes in the situation. (10) Between these two kinds of "stars" were noticeable differences in interaction patterns and the reasons for their being chosen by others.