The effects of several highly purified simple and mixed dietary triglycerides (TGs) on serum and liver cholesterol and on sterol excretion were studied in rats. The TGs contained 4- to 18-carbon fatty acids with melting points of -75 to 63.5 degrees C. Ratios of polyunsaturated to saturated fatty acids ranged from 0.1 to 105. Ratios of total unsaturated to saturated fatty acids ranged from 0.1 to 115. All diets contained 8% TG plus 0.82% safflower oil. Sterols were quantified directly by a new and improved high resolution gas chromatographic method and were identified by mass spectrometry. TG digestibilities correlated negatively with melting points above 30 degrees C (R = -0.9). Serum cholesterol was lower in rats fed tributyrin, tricaproin, tricaprylin, tricaprin, trielaidin, trilinolein or partially hydrogenated soybean oil (43-49 mg/dl) than in those fed trilaurin, trimyristin, tripalmitin, tristearin, triolein or corn oil (54-59 mg/dl). Liver lipid levels correlated (R = 0.65) with the degree of unsaturation of dietary TGs. Liver cholesterol levels correlated negatively with fecal excretion of coprostanol plus cholesterol (R = -0.4). Coprostanol plus cholesterol excreted in feces correlated weakly (R = 0.3) with intake of total sterol and of polyunsaturated TGs (R greater than or equal to 0.4 are at least 80% significant). The results demonstrate that consumption of polyunsaturated TGs was associated with higher hepatic lipid levels. Also, greater fecal excretion of coprostanol plus cholesterol was associated with lower hepatic cholesterol levels.