The albuminuria that frequently occurs in athletes after severe exercise has been observed not only in contact sports but also in sports like rowing, which are nontraumatic and certainly involve no body contact. This study concerns urinary findings after severe exertion at rowing, swimming, lacrosse, track, and football. The percentage of athletes having albumin, red blood cells, and casts in their urine after severe exercise was similar in all five sports. With respect to the finding of red blood cells, swimming, lacrosse, and track were about the same (80%), and football and rowing about even (55%). The 1,500-meter swimmers and the long distance track men showed the greatest amount of all three abnormal urinary findings. The duration of the event played a major part in determining the degree of the abnormality, and in the 1,500-meter race especially the urine was often loaded with red blood cells and casts. These usually disappeared within 24 hours, but the question is raised whether kidneys handicapped by previous infections can go through such experiences without cumulative damage.