Periodic albino mutant (ap/ap) of Xenopus laevis is a pigmentationmutation affecting pigment cells in the skin and pigment epithelium of the eye.It has been described that pigment epithelium, melanophores and iridophoresare abnormal, and that unusual leucophore-like cells develop as a part ofmelanophore lineage in this mutant. In the present study, differentiation ofiridophores and xanthophores was investigated using the neural tube culturesystem in various culture conditions, and the ultrastructures of differentiatedpigment cells were compared between the wild-type and the mutant. It is shownthat iridophores and xanthophores require different culture conditions fordifferentiation. In the periodic albino mutant, reflecting platelets of iridophoresare abnormal in size and shape. Pterinosomes are also abnormal in mutantxanthophores, and the pterinosome size is extremely large in the mutant. Thisis the first demonstration that detrimental effects on pigment organellogenesisare found in xanthophores, in addition to melanophores, iridophores, pigmentepithelium, and leucophore-like cells in the periodic albino. These findingsstrongly suggest that pigment organellogenesis is affected in all types of pigmentcells including unusual leucophore-like cells in the periodic albino. This mutantwould provide some insight for organellogenesis and development of variouspigment cells.