The lipid and lipoprotein metabolism was examined in fortyfour long distance runners and in a cohort of sixty-five untrained subjects as well as in thirty-two runners before and immediately after 38- and 40-kilometer runs respectively. There was observed a significant increase of high density lipoprotein cholesterol in the runners, whereas very low density lipoprotein cholesterol showed a marked decrease. The low density lipoprotein cholesterol/high density lipoprotein cholesterol quotient (arteriosclerotic quotient) was found to be markedly reduced in the runners. There was no statistical difference in total cholesterol and low density lipoprotein cholesterol between long distance runners following sports as a pastime and untrained subjects. Post-heparin lipase and the rate of lipolysis were markedly increased in subjects following sports as a recreation. Parallelisms were observable between lipid values and lipoprotein percentages determined by disk electrophoresis. The proportions of alpha-lipoprotein, beta-lipoprotein, and pre-beta-lipoprotein in runners were found to be increased, unchanged, and reduced respectively. The increase in alpha-lipoprotein was accompanied by a shift in the spectrum of alpha-lipoprotein subfractions. After the 38- and 40-kilometer run, respectively, there were determined an increase in TGL and very low density lipoprotein cholesterol and a decrease in both post-heparin lipase and rate of lipolysis. The other cholesterol parameters showed no significant variations after straining. Whereas Apo A, like high density lipoprotein cholesterol, did not change during running, Apo B showed a marked increase. The results were discussed with due consideration of those reported by other authors.