Eight international class lightweight rowers were examined to determine the efficacy of rehydrating with water following 24 h of dehydration on body fluid balance, metabolic function, and rowing performance. The rowers performed a maximal rowing trial on a Gjessing rowing ergometer (4200 revs, 3-kg resistance) while euhydrated (ET) and following partial rehydration (RT). Body weight was reduced using exercise together with food and fluid restriction over 24 h and was followed by consumption of 1.5 l of water over 2 h. Body weight decreased 5.16 +/- 0.14% (P < 0.05) and plasma volume decreased 12.5 +/- 1.4% (P < 0.05) after dehydration. Rehydration restored plasma volume by 6.02 +/- 0.62%. Rowing trial time increased significantly from 7.02 +/- 0.17 min for the ET to 7.38 +/- 0.21 min for the RT (P < 0.05). The net plasma lactate accumulation decreased significantly from 8.77 +/- 0.31 mmol.l-1 for the ET to 6.77 +/- 0.24 mmol.l-1 for the RT (P < 0.05). Glycogen content (glycosyl units) of the vastus lateralis decreased by 203.6 +/- 18.6 mmol.kg-1 DW during the ET compared with 139.9 +/- 13.4 mmol.kg-1 DW during the RT (P < 0.05). These results demonstrate that the dehydration/rehydration protocol reduced maximal rowing performance due to lowered plasma volume and decreased muscle glycogen utilization.