For a comparative study between swimming in swimwear (control-sw) and swimming in clothes (clothes-sw), oxygen uptake (VO₂) and ratings of perceived exertion (RPE) were measured. The subjects were six male members of a university swimming team. Three swimming strokes - the breaststroke, the front crawl stroke and the elementary backstroke - were applied. With regards to clothes-sw, swimmers wore T-shirts, sportswear (shirt and pants) over swimwear and running shoes. In both cases of control-sw and clothes-sw, the VO₂ was increased exponentially with increased swimming speed. The VO₂ of the subjects during the clothed tests did not exceed 1.4 times of that in the case of control-sw at swimming speeds below 0.3 m/s. As swimming speeds increased, VO₂ difference in both cases increased. Consequently, VO₂ in the clothed tests was equal to 1.5-1.6 times and 1.5-1.8 times of that in the swimwear tests at speeds of 0.5 and 0.7 m/s, respectively. At speeds below 0.6 m/s in clothes-sw, the breaststroke showed lower VO₂ than the front crawl stroke, and the elementary backstroke showed higher VO₂ than the other two swimming strokes. RPE increased linearly with %peak VO₂. In addition, any RPE differences among the three swimming strokes were not shown in the control-sw tests. At an exercise intensity above 60%peak VO₂, clothed swimmers showed slightly higher RPE in the front crawl stroke compared to that in the two other swimming strokes.