The present study examined lifestyle and behavioral correlates of the change in total testosterone over 13 years in 66 men aged 41-61 years who were former participants of the Multiple Risk Factor Intervention Trial (MRFIT) at the Pittsburgh, Pennsylvania, center. The authors also determined in these men if changes in total testosterone are related to changes in cardiovascular disease risk factors. The mean total testosterone level was 751 (standard deviation, 248) ng/dl at baseline and decreased by 41 (standard deviation, 314) ng/dl during follow-up. The correlation between measures was r = 0.44 (p < 0.001). In multivariate analysis, higher type A coronary-prone behavior score, greater pack-years of cigarette smoking, and the MRFIT special intervention group were associated with larger decreases in total testosterone. Age, body weight, weight change, leisure time activity level, and alcohol intake were not related to the change in total testosterone. The decrease in endogenous testosterone was associated with an increase in triglycerides and a decrease in high density lipoprotein cholesterol in multivariate analysis controlling for obesity and other lifestyle covariates. There was little relation between change in testosterone and change in total and low density lipoprotein cholesterol or blood pressure. This longitudinal study confirms a gradual decline in total testosterone levels with advancing age in older men and provides evidence that lifestyle and psychosocial factors are related to this decline. Decreases in endogenous testosterone levels with age in men are associated with potentially unfavorable changes in triglycerides and high density lipoprotein cholesterol.