Nearly 100,000 Gulf War veterans (GV) returned from the Persian Gulf reporting numerous symptoms with no apparent medical explanation. Of these symptoms, musculoskeletal pain was a primary complaint resulting in diminished physical function and quality of life. The purpose of the present investigation was to determine the cardiorespiratory and perceptual responses to exercise in GV with chronic musculoskeletal pain compared to healthy pain free GV. Thirty GV (n=13 muscle pain; n=17 healthy) completed an acute bout of cycling exercise to volitional exhaustion. Exercise intensity increased by 30 Watts every 3 min. Cardiorespiratory and metabolic variables were collected continuously. Leg muscle pain intensity (0-10) and ratings of perceived exertion (RPE: 6-20) were obtained during the last 15 sec of each minute. Psychophysical curve estimates were calculated for log transformed pain and RPE data to determine the growth function of pain and effort. There were no group differences in age, height, weight or self-reported physical activity. There were no group differences in oxygen consumption, heart rate, ventilation or respiratory rate during exercise. When expressed relative to each individual's exercise capacity, RPE were not significantly different between groups. However, GV with chronic muscle pain rated exercise as significantly more painful (p<0.01) than healthy GV. Psychophysical curve estimates indicated no differences for RPE (slope: 0.60 sick GV vs. 0.60 healthy GV). Curve estimates for pain (slope: 2.5 sick GV vs. 3.6 healthy GV) approached significance (p=0.08) with a large effect size between groups (d=0.70). Our results suggest that GV with musculoskeletal pain are not different in terms of cardiorespiratory and metabolic responses to exercise, and do not perceive exercise as requiring more effort than healthy GV. However, GV with chronic muscle pain do perceive exercise as more painful. Therefore, extra care should be taken when prescribing exercise for veterans with chronic musculoskeletal pain complaints.