The purpose of this study was to determine the relationship between oxygen demand, stroke rate and swimming velocity in competitive swimmers. The subjects who volunteered for this study were ten trained male swimmers (age, 16.7 +/- 0.4 yrs). VO2peak, swimming velocities at 80% (V80% VO2peak) and 100% (V100% VO2peak) of VO2peak and swimming velocity at the onset of blood lactate accumulation (VOBLA) were determined during a swimming economy profile test in a swimming flume. In the swimming economy test, determined by studying the relationship between oxygen uptake and swimming velocity cubed, the subjects were instructed to swim for six minutes at five or six submaximal swimming velocities. Steady-state oxygen uptake and stroke rate were calculated during the final two minutes of swimming. Results indicated that there were significant correlations between oxygen uptake and swimming velocity cubed (r = 0.963 to 0.998, p < 0.01), between oxygen uptake and stroke rate (r = 0.925 to 0.998, p < 0.01) and between stroke rate and swimming velocity cubed (r = 0.897, p < 0.05; to 0.994, p < 0.01) for all subjects. Furthermore, it was found that the slopes of the regression lines between oxygen uptake and swimming velocity cubed and between oxygen demand and stroke rate were significantly correlated to swimming performance indices (V80% VO2peak, V100% VO2peak and VOBLA). The results of this study suggest that the slope of the regression line between oxygen uptake and stroke rate can be utilized as an effective index of evaluating swimming performance.