Intensive physical exercise result in certain changes in the body, kidneys in particular. A total of 23 highly qualified sportsmen were investigated for plasma proteins in the urine before and after the graded bicycle ergometry. The impairment of renal reabsorption due to physical load was evidenced by significant amounts of albumin in the afterload urinalyses of all the examinees, and the appearance of IgG in urinalysis of 6 sportsmen in comparison to the urinalysis before the exercise which reported insignificant levels of albumin in 6 subjects only.