Three experiments were conducted to determine the affect of dietary manganese on cholesterol and lipid metabolism in avian species. In the first experiment, day-old chicks were fed a manganese-deficient (4.8 micrograms/g) and a manganese-supplemented (104.8 micrograms/g) diet for 4 weeks after which time they were injected with estrogen (5 mg diethylstilbestrol per kilogram body weight). Manganese deficiency did not significantly alter plasma or liver cholesterol in either group. Estrogen administration significantly increased plasma cholesterol concentration in both dietary groups and liver cholesterol in the manganese-deficient group. In the second experiment, 15-week-old White Leghorn pullets were fed a manganese-deficient (4.5 micrograms/g) diet for 10 weeks. Although dietary manganese deficiency significantly decreased hepatic manganese and cholesterol concentrations, it did not affect hepatic cholesterol and fatty acid synthesis, liver lipid, plasma or egg yolk cholesterol. Similar results were obtained in the third experiment with older (36-week-old) laying hens given similar manganese-deficient and adequate diets. These results indicate that dietary manganese deficiency in the avian species does not result in a significant alteration of cholesterol and lipid metabolism.