Serum cholesterol, high-density lipoprotein cholesterol, and triglycerides of three groups of Seventh-day Adventists (SDAs)--true vegetarians, lacto-ovo vegetarians, and nonvegetarians--and the general population were measured and related to age, sex, and diet. True vegetarian SDAs had the lowest cholesterol levels while cholesterol levels of the other three groups were similar. Triglyceride levels were highest in the true vegetarian SDAs and lowest in general population. Cholesterol levels rose with increasing age while percentage of high-density lipoprotein cholesterol fell. Female SDAs in all three dietary groups had higher cholesterol levels than males. In all four groups percentage of high-density lipoprotein cholesterol was higher in females than in males. In the male subjects, cholesterol levels varied linearly and inversely with carbohydrate intake. Protein and fat intake in true vegetarian SDAs and lacto-ovo vegetarian SDA groups were lower than in the nonvegetarian SDA and general population groups. The differences in protein and fat intake were reflected in elevations in serum cholesterol levels. In the female subjects, cholesterol levels were also inversely correlated with carbohydrate intake but not as distinctly as in the males. True vegetarian SDA females ingested less protein and fat than the other three groups and exhibited lower serum cholesterol levels. Cholesterol levels in lacto-ovo vegetarian SDA, nonvegetarian SDA, and general population female subjects were similar and did not reflect differences in protein or fat intake. The true vegetarian dietary lifestyle resulted in lowest cholesterol levels, however, if it was breeched to the least extent, cholesterol levels rose. Thus, intake of skim, low fat, or whole milk resulted in similar serum cholesterol levels as did low or high egg consumption.