The effects of three weight reduction methods on maximal strength, rate of force development, vertical jumping height, and mechanical power were studied in track and field athletes and volleyball players. The three methods were sauna, diet with diuretic, and diuretic alone. The reductions in weight achieved were 3.4%, 5.8%, and 3.8% of body weight after sauna, diet + diuretic, and diuretic, respectively (P less than 0.001). Maximal isometric leg strength and the rate of isometric force development were decreased after the sauna and diet + diuretic treatments. Dehydration caused by the diuretic method alone did not impair neuromuscular performances. As had been expected from theoretical calculations, the rise of the body center of gravity in vertical jumping was slightly improved with all three treatments, the improvement being the greatest following the diuretic treatment (7.1%, P less than 0.001). However, when the work performed was extended for 15 s, an improved power output could be observed only with the diet + diuretic treatment (P less than 0.01). No explanation for the results observed could be made in terms of physiologic parameters.