This study was conducted to compare bodyweight (bwt) loss and recovery in Standardbred horses receiving frusemide compared to controls. Thirty Standardbred horses from 7 training stables that were racing at the Red Mile in Lexington, Kentucky, during the spring 2001 pari-mutuel meeting were studied. Fourteen horses (FRU) received frusemide (250 mg/horse i.v.) 4 h prior to racing, while 16 horses (NFRU) did not received frusemide. Horses were weighed on the morning of race day, prior to warm-up, after racing and the next day. Changes in bwt were calculated as percentage increase or decrease from initial bwt. Prior to warm-up, FRU horses had a mean bwt reduction of 1.30 +/- 0.63%, (P<0.01), compared to a 0.19 +/- 0.63% increase for the NFRU horses. FRU horses had a greater (P<0.03) postrace bwt loss (3.55 +/- 0.55%) than the NFRU horses (2.71 +/- 0.66%). On the morning after racing, bwt was still below initial values by 0.90 +/- 0.55 and 1.24 +/- 0.35% for the FRU and the NFRU horses, respectively. While frusemide administration increased the postrace weight loss in racing Standardbreds, it did not affect short-term bwt recovery. Further research is required into management strategies required to allow horses to replenish fluids and electrolytes safely following strenuous exercise.