An interesting aspect, when comparing athletes, is the effect of specialized training upon both physiological performance and perceptual responses. To study this, four groups (with six individuals each) served as subjects. Two of these consisted of highly specialized individuals (racing cyclists and marathon runners) and the other two of non-specialized individuals (sedentary and all-round trained). Cycling on a cycle ergometer and running on a treadmill were chosen as modes of exercise. Variables measured included heart rate, blood lactate and perceived exertion, rated on two different scales. Results show a linear increase of both heart rate and perceived exertion (rated on the RPE scale) in all four groups, although at different absolute levels. Blood lactate accumulation, during cycling and running, differentiates very clearly between the groups. When heart rate and perceived exertion were plotted against each other, the difference at the same subjective rating (RPE 15) between cycling and running amounted to about 15-20 beats.min-1 in the non-specialized groups. The cyclists exhibited almost no difference at all as compared to 40 beats.min-1 for the runners. It can be concluded that specialized training changes both the physiological as well as the psychological response to exercise.