The effect of an aqueous extract of Carica papaya seeds (5 mg/kg body/day im and 20 mg/kg body wt/day oral) were investigated in male mice treated for 60 days. Reversibility studies were also carried out to elucidate if any induced effects were transient. The aqueous extract did not manifest any estrogenic effects in male mice, and LD50 studies indicated its nontoxic nature. The body weight or the weights of reproductive organs, kidney, and adrenal were not affected, indicating that the extract did not promote body weight gain through obesity or water retention. The serum SGOT, SGPT, protein, and cholesterol levels were also within the normal range in the extract-treated mice, suggesting that the extract does not influence liver function or cholesterol and protein metabolism. These data suggest that the aqueous extracts of papaya seeds is safe and could serve as an effective male contraceptive in rodents.