The effects of injected aminopterin (0.02mg/female) on oogenesis in cockroach, panoistic ovariole. were studied by histological and histochemical methods. In ovaries fixed one day after injection, the follicle cell and ooplasm of matured oocytes were vacuolated and the nuclei of some of the follicle cells were clumped. In ovaries fixed 6-7 days after injection, prefollicular nucleus and chromatin of follicle cells in unmatured oocyte were also clumped. In matured oocytes, vacuolated cytoplasm and nuclei of follicle cells were degenerated, and the follicle cells surrounding the oocyte was disorganizated. The degenerating oocytes and follicle cells failed to stain with mercury bromphenol blue, therefore, aminopterin may affect the inhibitors for protein synthesis and DNA synthesis in the follicle cell. The degenerating oocytes exhibited a concentration of lipid in the remnant yolk and contained to weak positive granules for PAS reaction.