The absorption and metabolism of 4-C14-cholesterol by nymphal German cockroaches (Blattclla germanica (L.)) was studied after two weeks on diets containing 0.05% C14-cholesterol with and without the sterol antagonist, cholesteryl chloride, at a 1:10 ratio. Dietary cholesterol was efficiently utilized when fed alone, with greater than 90% of the ingested sterol retained. Cholesteryl chloride caused only about a 9% to 11% decrease in cholesterol utilization, as determined from the relative amounts of C14 compounds present in the roaches and their excreta. About 93% of the C14 compounds from the roadies behaved chromatographically as free sterols, 5% as esters, and the remainder as more polar compounds. Analyses of the free and esterified sterols by column chromatography and reverse-isotope dilution demonstrated that unchanged cholesterol accounted for 95% of these fractions and another 2.5% behaved like 7-dehydrocholesterol. Xo significant amounts of either C14-labeled bile acids or coprostanol were detected in the excreta.