Dehydration, a common practice among competitive athletes in sports including weight classes, has uncertain effects on strength. This study examined the effects of passive dehydration (D, approximately 2 hours in a sauna) followed by rehydration (R, approximately 2 hours of rest with water ad libitum) on bench press one-repetition maximum (1RM). Ten weight-trained males (x +/- SE; age = 25 +/- 1 years; mass = 85.5 +/- 5.2 kg; height = 173.5 +/- 1.7 cm; body fat = 17.8 +/- 2.2%; 1RM = 118 +/- 8 kg) completed 2 testing sessions (E1/E2 and D/R) consisting of, respectively, 2 euhydration 1RM measurements separated by 2 hours of rest; and D 1RM followed by R 1RM. Testing sessions were administered in counterbalanced order and separated by 1 week. D resulted in increases (p < 0.005) in body temperature, urine specific gravity, hematocrit, and hemoglobin (calculated 8% decrease in plasma volume) as well as decreased body mass (p < 0.005). 1RM was decreased following D (111.4 +/- 7.2 kg) compared to both E1 (118 +/- 7.6 kg, p = 0.0015) and R (117.3 +/- 7.8 kg, p = 0.0023), with no significant difference between E1 and R. A significant association (r = -0.67, p < 0.05) was observed between percent lean body mass (%LBM) and the change in 1RM following D. In conclusion, passive dehydration resulting in approximately 1.5% loss of body mass adversely affects bench press 1RM performance. The adverse affects of dehydration seem to be overcome by a 2-hour rest period and water consumption.