Eight male varsity ice hockey players were studied during 4 hockey games to investigate the alteration in blood substrates and the depletion pattern of glycogen in the fibers of the vastus lateralis muscle. Venous blood was sampled before and after each period and biopsies were taken prior to and immediately following each game. Significant elevations (p less than 0.05) in blood glucose, lactate and plasma FFA occurred following each period with little difference shown between the periods. Muscle glycogen declined an average of 60%. The histochemically determined glycogen depletion pattern indicated utilization of Type I, IIA and IIB fibers, with the greatest depletion occurring in the Type I fibers. In spite of the differences between forwards and defensemen in the length and number of shifts, the blood substrate profile, amount and pattern of glycogen depletion were similar.