Abstract: The effects of ingestion of trivalent (chromium chloride) and hexavalent (potassium dichromate) chromium compounds were investigated on social aggression and fertility in male mice. Prepubertal male mice were exposed to these salts in drinking water at concentrations of 1000 and 5000 ppm for 90 days. The exposure of male mice to chromium chloride at 1000 or 5000 ppm significantly augmented social aggression. Fertility was significantly reduced in males exposed to the hexavalent chromium compound. The number of implantation sites and the number of viable fetuses in females impregnated by males exposed to this compound were significantly reduced. The exposure of male mice to the trivalent chromium compound had, however, no effect on fertility. Body, testes, preputial gland and seminal vesicle weights were significantly suppressed in males exposed to the hexavalent compound but no such effects were evident in mice given the trivalent chromium compound. The results show that the ingestion of trivalent and hexavalent chromium compounds by male mice in prepubertal life have very different effects on both social aggression and fertility. Only potassium dichromate produced a pattern of responses clearly indicative of suppressed gonadal function.