The purpose of this study was to examine the relationship between resting platelet count and levels of physical fitness as determined by the Harvard step test. It was hypothesized that the two variables are inversely related. Platelet counts and Harvard step test scores were obtained from 102 male subjects. Blood samples were obtained via fingertip puncture and the platelet count assessed by means of the Brecher-Cronkite method. The step test was performed in a controlled environment room. A Pearson product-moment correlation coefficient was calculated for resting platelet counts and fitness scores and found to be significant (P < .05). It was shown, however, to lack predictive power. A subsequent test for linearity, i.e., eta, failed to achieve significance. The subjects were sorted into high, moderate, and low fitness groups on the basis of their step test scores. A one-way analysis of variance revealed no difference between these groups. Finally, attest was performed between the platelet counts of the extremes of the fitness distribution. No difference was revealed. It was concluded within the limits of this study that there is no relationship between resting platelet count and physical fitness level, as determined by the Harvard step test.