The present study assessed the effect of high versus low palmitic acid intakes of plasma lipoprotein cholesterol levels and on rates for endogenous synthesis of cholesterol in normal and hypercholesterolemic subjects. On day 21 of each diet treatment, a fasting blood sample was drawn for lipoprotein determination and to provide a measure of the background level of deuterium. A priming dose of deuterium was consumed and a second blood sample obtained 24 hours after the first sample. Isotope ratio mass spectrometry was used to determine the incorporation of deuterium into the newly synthesized cholesterol molecule and fractional synthetic rates were calculated. Four diets were formulated to provide combinations of two levels of 16:0 at two levels of 18:2n-6. Subjects received each of the four diet treatments for 21 days, followed by washout periods of 21 days. Serum total cholesterol and LDL-cholesterol was not significantly affected by the high level of 16:0 when diets also contained a high level of 18:2n-6. Fractional synthesis rates of cholesterol observed for each diet treatment did not differ significantly, suggesting no relationship between the endogenous synthesis of cholesterol and dietary 16:0 content. The results indicate that 16:0 has no effect on serum lipoprotein profiles in the presence of recommended intakes for 18:2n-6.