The effect of strenuous exercise on lipoprotein level and composition as well as on lipoprotein lipase activity (LPLA) and glycogen stores in skeletal muscle was studied in 16 healthy young men after military field maneuvers. Body weight was reduced by 1 kg after the maneuvers and was gradually restored during a 5-day recovery phase. Glycogen levels were reduced by 50% and LPLA increased threefold immediately after the exercise, and neither were restored until 3–5 days of recovery. Serum triglycerides were decreased by about 50% after 1 day of recovery and the cholesterol concentration in high-density lipoproteins increased but only immediately after exercise. In contrast, the apolipoproteins A-I and A-II, the main protein constituents, were both decreased and remained so for 3–5 days. The results indicate that significant alterations of plasma lipoprotein level and composition as well as of muscle metabolism occur after prolonged physical exertion and that some changes are still evident after 5 days of recovery.