BACKGROUND This study examined physiological responses during 0% and 10% inclined treadmill exercise at prescribed ratings of perceived exertion (RPE) using the perceptual estimation-production paradigm. METHODS RPE's were estimated during a Bruce treadmill test to volitional exhaustion. Subjects then produced individually prescribed RPE's (associated with 50% and 70% VO2max) during level (0% grade) and inclined (10% grade) treadmill exercise. Heart rate response (HR) and oxygen consumption (VO2) were compared between estimation (EST), level production (LPR), and incline production (IPR) trials using one-way repeated measures ANOVA. Results were considered significant at < or = 0.05. RESULTS At 50% VO2max, HR and VO2 were not significantly different between EST (134 +/- 13 b x min-1, 27.1 +/- 5.6 ml x kg x min-1) and IPR (139 +/- 18 b x min-1, 30.6 +/- 11.2 ml x kg x min-1). However, HR and VO2 during LPR (123 +/- 20 b x min-1, 24.3 +/- 8.8 ml x kg x min-1) were significantly lower than IPR. For 70% VO2max, HR and VO2 were not significantly different between EST (168 +/- 9 b x min-1, 42.1 +/- 9.4 ml x kg x min-1) and IPR (169 +/- 14 b x min-1, 41.1 +/- 10.2 ml x kg x min-1). However HR and VO2 during LPR (155 +/- 17 b x min-1, 35.1 +/- 8.1 ml x kg x min-1) were significantly lower than during EST and IPR. CONCLUSIONS Results suggest physiological responses during RPE estimation-production trials correspond better when estimation and production trials were performed at a similar treadmill incline. For exercise prescription purposes, RPE estimations made during inclined treadmill exercise may require adjustments to achieve appropriate intensities during level treadmill exercise.