An investigation was carried out on 77 steelworkers, divided into two groups, at their work places. Group I (30 subjects) drank ad lib. a special tea containing (17.1 mmol/l NaCl, 1.34 mmol/l KCl, 0.14 mmol/l Na2HPO4, and 0.57 mmol/l vitamin C). Group II (47 subjects) drank ad lib. ordinary drinks (water, mineral water, and soda-water). Determination of water balance was performed seven times in all within 3 weeks. In groups I and II sweat losses were 5.1 +/- 1.2 kg and 5.0 +/- 1.3 kg, and intakes were 4.1 +/- 1.1 kg and 3.4 +/- 1.1 kg, respectively. When the intake period of the drinks with salts was extended it was found that voluntary dehydration decreased and amounted to 10% of sweat rate on the last day of the study. The voluntary dehydration in group I was lower by 40%, the difference being highly significant in comparison with group II (P < 0.001). Data obtained from anamnesis and a questionnaire results showed smaller fatigue, higher work capability and better subjective feelings in group I. Five subjects who previously had complained of recurrent pain and muscle spasm experienced disappearance of these symptoms. The importance of intake of water containing salts in hot working conditions and their role in maintaining the water-electrolyte balance for normal physiological functions and subjective feelings were discussed.