Twenty-six male and twenty-four female volunteers were studied with respect to serum-free and total cholesterol, the rate of serum cholesterol esterification, and serum LCAT levels. The rate of serum cholesterol esterification showed a lack of strong correlation with age in both female (r = 0.031) and male (r = 0.26) subjects. Better correlation in both sexes was found between the levels of serum-free cholesterol and the rate of its esterification (r = 0.78 for males, r = 0.5 for females). LCAT enzyme levels also correlated poorly with age in male (r = 0.0424) and in female subjects (r = 0.174). Enzyme levels showed a strong correlation with serum-free cholesterol in male (r = 0.785), but not in female subjects (r = 0.395). Serum cholesterol esterification was significantly higher in males than in females (p < 0.05) and the fractional rate of esterification (percentage of esterification per minute) showed even greater differences between the two sexes (p < 0.001).