To provide information on the duration of the regeneration phase after several hours of physical strain, venous blood samples of eight participants in a 1/4 triathlon competition were taken each day at the same time (arrival) for determinations of testosterone (T), SHBG, and cortisol (C). In addition, urea, creatinine, creatinine kinase, and the changes in plasma volume were determined. Directly after arrival, T had not changed substantially, but decreased nonsignificantly on each of the following days and obtained the lowest concentration on the 2nd day after the triathlon. T/SHBG as an expression of free testosterone was significantly reduced on the 2nd, 3rd, and 4th days after the competition. C increased up until the end of the competition by 4.5 times the original value, and during the subsequent days it decreased again to the normal range. Until the end of the observation period on the 4th day after the competition, urea was still significantly elevated. The data suggest an anabolic deficit lasting for several days as a result of prolonged physical strain.