Ten human adult males' usual diets were modified by incorporating 681g nonfat, unpasteurized yogurt daily throughout three 1421 day periods. A different set of select culture strains, two commercial and one patented, were used for yogurt production in the three dietary periods. Including yogurt daily in the diet significantly reduced fasting total serum cholesterol l&12% in human adult males on some days, but serum cholesterol returned towards control values with continued yogurt consumption. Serum triglycerides and the proportions of serum lipoproteins were not significantly influenced by increasing yogurt consumption. Differences in concentrations of uric, erotic and hydroxymethylglutaric-like acids in the yogurts were insufficient to account for the differences in temporary hypocholesterolemic effects of yogurt consumption seen between strains.