The present study of the diffusion process of "weed killer" PCP is a part of a series of study conducted by the writers in an attempt to develop a general theory of diffusion process from the point of view of communication science. For the past twelve years, the writers have been involved studies of the diffusion process of innovation in various rural communities of Japan, and these studies have been directed toward elucidating the following three questions, which the writers feel to be most important in developing a general theory. 1. To what extent factors of diffusion found in studies conducted in foreign countries, can be applied to diffusion process of innovation within Japanese rural communities. 2. What is the basis for certain factors to be applicable to the diffusion process of innovation within Japanese rural community and for the others to be not applicable. 3. What is the impact of diffused innovation upon the social system. Some of the studies conducted by the writers and prominent results of each study can be seen in the following. 1. CHRYSANTHEMUM CULTIVATION : The rate of diffusion process was dependent upon the amount and effect of mutual communication among relatives and neighbors. 2. GENTIAN CULTIVATION: The rate of diffusion process was dependent upon the influence of the local political leader in rationally promoting the innovation. 3. WEED KILLER 2,4-D, PCP: The rate of diffusion process was dependent upon the activities of change agents. 4. DURABLE CONSUMPTION GOODS (TV set and others): The rate of diffusion process was dependent upon the promotional activities of salesmen and manufacturers. 5. CHIKUMA (improved breed of rice): The rate of diffusion was influenced by agricultural crisis, namely agricultural damage resulting from cold weather. 6. MEMBERSHIP AFFILIATION WITH A NEW RELIGION : The rate of diffusion was dependent upon the promotional activities of marginal farmers employed in the nearby city. 7. SMALL SIZE FARM TRACTORS: The rate of diffusion was influenced by the low-interest government loan given to each farmer for the purchase of tractors. In this present study, the diffusion process of weed killer, known by the name of PCP., was investigated. The study was conducted in a small rural community of 146 households by the name of Minami Majino village which is located in Konami-Ku, Suwa-city, Nagano Pref., Japan, and the primary aim of this study was to test the applicability of various hypotheses of diffusion process developed by various foreign sociologist to the diffusion process of PCP in Minami Majino. The following hypotheses derived from studies of diffusion process in various foreign countries were tested in Minami Majino village. Hypothesis 1-1. Impersonal information sources are most important at the awareness stage. 1-2. and personal sources are most important at the Hypothesis 2. evaluation stage in the Adoption Process. Cosmopolite information sources are most important at the awareness stage, and Localite information sources are most important at the evaluation stage. Hypothesis 3. Impersonal sources of information are more important than personal sources for relatively earlier adopters of innovations than for later adopters. Hypothesis 4. Cosmopolite sources of information are more important than Localite sources for relatively earlier adopters of innovations than later adopters. Hypothesis 5. The first individuals to adopt innovations require a shorter adoption period than do relatively later adopters. Hypothesis 6. The awareness-to-trial period is longer than the trial-to-adoption period. Hypothesis 7. The awareness-to-trial period is shorter for relatively earlier adopters than later adopters. Hypothesis 8. The trial-to-adoption period is longer for relatively earlier adopters than for later adopters. Hypothesis 9. Adopter distributions follow a bell-shaped curve over time and approach normality. Hypothesis 10. Awareness proceeds at a more rapid rate than does adoption. Hypothesis 11-1. Earlier adopters are younger in age than later adopters. 11-2. Earlier adopters have higher social status than later adopters. 11-3. Earlier adopters have a more favorable financial position than later adopters. 11-4. Earlier adopters have more specialized operations than later adopters. Hypothesis 12-1. The sociometric leaders are more innovative than followers. 12-2. Pairs of sociometricly related individuals adopt the innovation at about same time. Of the above hypotheses, H1-2, H2, H3, H4, H5, H6 and H7 were applicable to the diffusion process of PCP in Minami Majino village. H1-1, H8, H9, H10, H11-1, H11-2, H11-3, H11-4, H12-1 and H12-2 were not applicable. The writers have found that so many hypotheses were not applicable to the diffusion process of PCP in Minami Majino village.