In 30 rowers plasma growth hormone and cortisol responses to a 7-min test on a rowing apparatus, performed at the highest possible rate, or to a competition race of 2000 m were recorded three times during a period that lasted up to 20 months. Apart from an improvement of the results in competition the increased performance capacity was also indicated by means of power output during the 7-min test (from 363 +/- 8 to 425 +/- 7 W in group A and from 382 +/- 7 to 437 +/- 9 W in group B). A pronounced rise was found in pre-exercise (in group A) and post-exercise (in both groups) cortisol levels. Post-exercise growth hormone levels increased when the rise in the mean power output was 40 W. Significant correlations were revealed between group values of power output and hormone levels during the study period. The performance capacity correlated with growth hormone levels after competition. The highest values were found in 10 elite rowers, studied additionally during an international competition. In cortisol values this kind of dependence was not found. Only the pre-competition concentrations of cortisol were significantly higher in elite rowers than in rowers of lower performance levels. Thus a further improvement of the performance capacity in previously trained sportsmen is associated with elevated growth hormone and cortisol levels in supramaximal exercises.