Gossypol is a toxic factor indigenous to the cotton plant genus Gossypium. Concentrations of free gossypol contained in feedstuffs such as whole cottonseed and cottonseed meals vary considerably. Nonruminant animals are particularly sensitive to the toxic effects of gossypol, whereas ruminants are somewhat more resistant. Signs of gossypol toxicosis in nonruminants, preruminants, and ruminants are similar and include labored breathing, dyspnea, decreased growth rate, and anorexia but are not pathognomonic. Postmortem findings include generalized edema and congestion of lungs and liver, fluid-filled thoracic and peritoneal cavities, and degeneration of heart fibers. The antifertility effect observed in many nonruminant species is overshadowed by toxic effects, particularly in females. Gossypol seems to disrupt estrous cycles, pregnancy, and early embryo development in females of all nonruminant species studied. Probable mechanisms include an endocrine effect on the ovary as well as a cytotoxic effect on the uterus or embryo. The female ruminant seems to be relatively insensitive to the antifertility effect of gossypol; however, in vitro data indicate some inhibition of embryonic development and ovarian steroidogenesis. The antifertility effect of gossypol has been studied most in males of nonruminant species. The effects of gossypol in the male are both dose- and time-dependent. At effective doses, gossypol causes males to be infertile because of sperm immotility and depressed sperm counts. Specific mitochondrial damage in the tails of spermatozoa seems to render them immotile, and extensive damage to germinal epithelium may be responsible for depressions in spermatogenesis. In ruminant males fed diets containing gossypol, ejaculated sperm appears normal under light microscopy. The integrity of the membrane of sperm cells may be damaged. Extensive damage to the germinal epithelium has been shown in both rams and bulls fed diets containing gossypol and is of major concern.