Tolnidamine belongs to the chemical class of 1H-indazole-3-carboxylic acids. These agents exert antispermatogenic activity and have two cell targets, Sertoli cells and germ cells, in the seminiferous epithelium. Tolnidamine medication induced irreversible inhibition of spermatogenesis. The addition of tolnidamine at the beginning of the culture period reduced the plating efficiency of Sertoli cells; however, tolnidamine did not induce a significant change in cell number if it was added 24 h after plating of the cells. Sertoli cell-enriched cultures prepared from tests of 10-day-old rats were highly sensitive to tolnidamine as evidenced by a marked inhibition in secretions of androgen binding protein, testibumin and transferrin. A 4-week study has been conducted in rhesus monkey fed tolnidamine orally. Dosages of 200 mg/kg and 400 mg/kg produced aplasia of the germinal epithelium with abnormal renal function.