The distributions are described of lipids and lipoprotein cholesterol in a randomly selected sample from a Minneapolis, Minnesota, suburb. There are large differences in these levels in different age, sex and hormone use groups. Total plasma cholesterol, the low-density and very-low-density lipoprotein fractions, and plasma triglycerides rise steadily for ages 10-49 in both men and women. The level continues to rise in women during ages 50-59 but falls in men. High-density lipoprotein cholesterol, however, decreases from sexual equality at ages 10-11 to low levels in adult men. High levels are maintained in adult women. Exogenous hormones apparently affect lipids. Oral contraceptive use is associated with higher levels of each of the lipids except high-density lipoprotein cholesterol; post-menopausal supplementary estrogen use is associated, however, with decreased total and low-density lipoprotein cholesterol levels, while the high-density fraction is higher.