Mancozeb a carbamate fungicide was administered orally at doses of 500, 600, 700, and 800 mg/kg/day to normal hemicastrated virgin rats for 15 consecutive days to examine the effect on ovarian hypertrophy. Sham-operated and hemicastrated control rats were administered a similar quantity of olive oil. The vaginal smear and body weight of the rats were recorded daily and rats were sacrificed on the Day 16. The ovary, uterus, kidney, adrenal, spleen, liver, lungs, heart, thymus, and thyroid were removed and weighed. The left ovary from each animal was serially sectioned and stained for histologic studies. The hemicastrated control rats revealed a significant increase in relative ovarian weight with 66.3% hypertrophy. Treatment with 700 and 800 mg/kg/day mancozeb revealed a decrease in ovarian hypertrophy with 28.2 and 22.8% hypertrophy, respectively. There was no significant change in the number of estrous cycles and duration of each phase of the estrous cycle with 500 mg/kg/day mancozeb. However, there was a decrease in the number of estrous cycles, duration of proestrus, estrus, and metestrus with concomitant significant increase in the duration of the diestrus phase with 600, 700, and 800 mg/kg/day mancozeb treatment. There was a significant decrease in the number of healthy follicles with concomitant increase in the number of atretic follicles at higher doses of mancozeb. There were no significant changes in the body and organ weight with 500, 600, 700, and 800 mg/kg/day of mancozeb. The levels of protein, glycogen, total lipid, phospholipid, and neutral lipid were elevated in the liver, uterus, and ovary after hemicastration. Protein, glycogen, total lipid, phospholipid, and neutral lipid were not significantly changed in the liver, uterus, and ovary after 500 mg/kg/day mancozeb. However, treatment with 600, 700, and 800 mg/kg/day mancozeb showed a significant decrease in the levels of protein, glycogen, total lipid, phospholipid, and neutral lipid in the liver, uterus, and ovary, with the exception of liver total lipid and uterine glycogen. In addition to the decrease in the compensatory ovarian hypertrophy, mancozeb treatment reduced the number of healthy follicles with a concomitant increase in the number of atretic follicles. This finding plus disruption of the estrous cycle may be due to a direct effect on the ovary or the hypothalamo-hypophysial-ovarian axis.