In a prospective, controlled study, the influence of strenuous physical exercise on plasma total cholesterol, HDL cholesterol, apolipoprotein A-I, total triglycerides and fatty acid composition of adipose tissue was studied during 7 months of training in 15 senior oarsmen and 21 controls matched for age, smoking and drinking habits. Dietary intake was monitored. At the start of the study there were no differences in lipid parameters and adipose tissue composition between oarsmen and controls. A significant decrease in total cholesterol and total triglycerides and an increase in HDL cholesterol and apolipoprotein A-I was noted in the oarsmen after only 2 weeks of training. Body weight remained stable but skin-fold thicknesses decreased. Food consumption increased considerably but diet composition remained unchanged Nevertheless the fatty acid pattern of adipose tissue changed significantly, as a result of altered preferential endogenous fatty acid synthesis and/or fatty acid oxidation. Since lipid parameters and adipose tissue composition were equal in oarsmen and controls before the start of the training, it is concluded that the changes induced by exercise only last for the duration of the training period.