In this study, the effects of mono(2-ethylhexyl) phthalate (MEHP), one of metabolites of di(2-ethylhexyl) phthalate, on immature Shiba goat testes in vitro were examined. The testes of 2-month-old Shiba goats were cut into smaller pieces, and seeded in medium. At 1, 3, 6 and 9 hr after administration of MEHP at various concentrations (0, 100 nmol ml-1, 1 nmol ml-1, and 1 x 10-3 nmol ml-1, respectively), the specimens were obtained for light and transmission electron microscopic observations. As a result, at 1 hr after exposure to MEHP, the vacuolization and nuclear membrane rupture appeared in Sertoli cells. Such alterations tended to gradually increase in number in timeand dose-dependent manners. Moreover, by MEHP treatment, apoptotic spermatogenic cells (characterized with chromatin condensation, cytoplasm shrinkage without membrane rupture, still functioning cell organelles, and packed cell contents in membrane-bounded bodies), apoptotic Sertoli cells (characterized with nuclear membrane lysis, nuclear condensation), necrotic spermatogenic cells (characterized with swollen and ruptured mitochondria, plasma membrane lysis, spilt cell contents, and chromatin clumps), and necrotic Sertoli cells (characterized with marginated chromatins along the nuclear membrane, ruptured vesicles within the MNB, some swollen and ruptured cell organelles, e.g. mitochondria) could be identified. Conclusively, ultrastructurally the treatment with MEHP at low concentration tends to lead spermatogenic and Sertoli cells to apoptosis, whereas that at high concentration tends to lead spermatogenic and Sertoli cells to necrosis. Thus, the testicular tissue culture is advantageous for screening testicular toxicity of chemicals.