In 7 men and 5 women, we measured the amounts of sweat and fluid intake, and the ionic composition of sweat during a 3-hour badminton practice in summer. The amount of sweat was calculated as follows; body weight before practice (g)--body weight after practice (g)--urine volume (ml) +fluid intake (ml). We collected sweat by covering the non-dominant forearm with a plastic bag. The amounts of sweat and fluid intake during the 3-hour practice were 1809 +/- 715ml (mean +/- SD) and 658 +/- 344ml, respectively. Weight loss after the practice was 2.0 +/- 0.9% of their weight before the practice. The Na(+) and Cl(-) levels of the sweat about 30 min after the start of practice were 66 +/- 34 mEq/l and 54 +/- 32mEq/l, respectively. There was no significant difference between those ionic levels of the sweat about 30 min after the start of practice and those about 30 min before the end of practice. The sum of Na(+) and Cl(-) loss into sweat during a 3-hour practice session was supposed to be 6.9 +/- 5.3g, and to be above 10 g in 4 of 7 men, assuming that there were no regional differences in the ionic composition of sweat. The findings suggested that most of the participants should take more fluid and some of them might need salt intake during the practice.