Fourteen elite swimmers had measurements of stress hormones taken at five points during a 6-month season: early-, mid- and late-season, during tapering for National Trials, and 1-3 d after the Trials. Training details and subjective ratings of fatigue were recorded daily in log books. Plasma norepinephrine and epinephrine concentrations were significantly correlated with swim training volume (r = 0.37 and 0.33, respectively, P < 0.05 for each). No significant differences were seen in norepinephrine or cortisol concentrations at the five sampling times. Epinephrine levels were significantly lower (P < 0.05) after competition compared with values early in the season and shortly before competition. Symptoms of the overtraining syndrome were identified in three of the swimmers, based on performance decrements and high, prolonged levels of fatigue. In these three swimmers, norepinephrine levels tended to be higher than those of the other swimmers from mid-season onward and were significantly higher (P < 0.01) during tapering. If these findings can be confirmed in larger numbers and different types of athletes, norepinephrine level may provide a useful marker of the overtraining syndrome.