Serum muscle enzyme levels, myoglobin levels, and renal function were measured in a group of 20 army recruits who had volunteered for a prolonged period of primary, specially designed, gradual training. Blood samples were taken before training and before and after each hike. Levels of serum myoglobin, creatinine phosphokinase, lactic dehydrogenase, and SGOT indicated muscle injury. Levels of urea creatinine, and uric acid and creatinine clearance evaluated renal function. Substantial elevation of muscle enzyme levels and persistent myoglobinemia were observed throughout the study. A highly significant decrease in creatinine clearance was demonstrated. After the last hike, the mean creatinine clearance was 70.41 mL/min, which is notably lower than the value at the beginning of the study. Prolonged physical exercise induces muscular damage, as evidenced by a rise in myoglobin and enzyme levels. Continuous muscle injury induces persistent myoglobinemia, a probable hazard to renal function.