This study assessed the reliability of ratings of perceived exertion (RPE) for the prescription of exercise intensity during cycling. Ten healthy men (21 to 62 years) and six women (25 to 50 years) attended the laboratory four times, 5 to 7 days apart. On the first visit each subject's maximal oxygen uptake was measured and, subsequently, they cycled at constant work rates based on their perception of ratings 9, 13 and 17 of the Borg 6-20 scale by regulating the resistance of the ergometer without reference to the instrument display panel. Analysis of variance revealed no significant between-trial differences with regard to oxygen uptake (VO2) or heart rate for men or women. The relative exercise intensities corresponding to the 3 ratings of exertion did not differ between men and women. Between-trial correlations for VO2 were highest for visits two and three at RPE levels 9 and 13 (r = 0.83 and r = 0.94) and consistently high (r = 0.92 or greater) for the three trials at RPE17. These data suggest that RPE is a useful frame of reference for the regulation of high levels of exercise intensity in healthy men and women. Small amounts of practice with the scale improve its applicability at lower exercise levels.