<bold>Purpose.</bold> The purpose of this research was to determine the relationship between a tennis players' technical abilities and their capacity evaluated in both a laboratory and on the tennis court. <bold>Basic procedures.</bold> Twelve tennis players participated in the study. The anaerobic capacity test (Wingate) and the progressive test were performed on a Monark E 895 cycloergometer. The aerobic and anaerobic capacities were evaluated in the laboratory. The Weber capacity test was performed on a tennis court. <bold>Main findings.</bold> The research did not reveal any significant correlation between the Wingate's mechanical parameters and the physiological parameters of the Weber test. A correlation of the maximal oxygen uptake with stroke precision on a tennis court can be observed. The research found that the maximal power output (Pmax) and total work (Wtot) found in the laboratory is related to the stroke precision on a tennis court. <bold>Conclusions.</bold> The results may suggest that both tests can be applied in the assessment of capacity and the effects of training. From the results of the laboratory and on-court tests, it is possible to specify a player's semi-specific endurance.