The aim of this study was to investigate the existence of a relationship between performance capacities and blood levels of testosterone (T) and cortisol (C). Thirty-two professional soccer players volunteered for the study. Morning levels of hormones were plotted against results of maximal vertical jump with a preparatory counter-movement (CMJ), 30 m running, and Cooper's 12-min running test. The serum T was positively related to both CMJ and average running speed (r=0.43 and r=0.47, respectively). Serum levels of C and T were in negative correlation (r= -0.40 and r= -0.49, respectively) with the results of Cooper's test. It was concluded that athletes with better explosive strength and sprint running performances have a higher basal level of testosterone. The results suggest a relationship between testosterone production and development of fast twitch muscle fibres in athletes.