To determine the influence of body composition upon swimming performance with and without wetsuits, 14 competitive female swimmers (mean (s.d.) age, 19.9 (0.9) years) were measured for body density while wearing both wetsuits and normal swimsuits. Subjects swam 400 and 1500 m trials with and without wetsuits, randomly, over a 12-day period. Six subjects participated in an additional trial while wearing neoprene leg-bands fitted over the wetsuit. Mean (s.d.) subject density without and with wetsuits was 1.048 (.009) and 1.021 (.007) g/ml respectively. Wetsuits reduced (P less than 0.05) swim times for the 400 (-4.96%) and 1500 m swim (-3.23%) compared with swimsuit trials. The neoprene bands increased (P less than 0.05) swim times relative to swimsuit and wetsuit trials. With wetsuits, swim times were inversely (P less than 0.05) related to density for the 400 (r = -0.46) and 1500 m swim (r = -0.54) suggesting that wetsuits increase performance by increasing buoyancy and that lean subjects benefit more from wearing wetsuits than do fatter subjects.