We investigated the association of plasma high-density lipoprotein (HDL) cholesterol levels with levels of cholesterol in other plasma lipoprotein fractions (low-density [LDL], very low density [VLDL] and their sum) and with total plasma cholesterol and triglyceride levels in 3493 males and 3318 females in the Lipid Research Clinics (LRC) Prevalence Study. Correlation coefficients were calculated for each stratum of age, sex and hormone use using a logarithmic transformation. The correlations of log HDL cholesterol with the other lipid and lipoprotein fractions generally depended strongly on age and sex but not on use of gonadal hormones. In the 20-70-year range, the age dependence of each correlation coefficient was well described by a linear regression model. The weakly positive association between HDL and total cholesterol levels in adults and the marked negative association of HDL cholesterol with triglyceride and VLDL cholesterol levels in almost all strata are in good general agreement with the results of earlier studies.