The present study examined the reproducibility with which subjects with stable chronic obstructive pulmonary disease (COPD) scale the sense of effort involved in breathing during exercise. The sense of effort was assessed in 6 subjects with COPD during bicycle exercise continued to a symptom-limited maximal work load using a conventional category scale. Reproducibility of the sensory experience was assessed by comparing results obtained from 3 incremental work tests, 2 on the same day and a subsequent test performed within 1 to 10 days. During all trials in all subjects, sensory scores correlated closely with both minute ventilation and oxygen consumption (r greater than or equal to 0.92 for both VE and VO2). The average coefficients of variation for the maximal Borg Score and Borg Score at 2 min of exercise for the group as a whole were 3 +/- 1 and 3 +/- 2% (SE), respectively. Variability in sensory scores was not significantly different on exercise trials performed either within or between days. Furthermore, variability of sensory scores, oxygen consumption, heart rate, or minute ventilation were similar. We conclude that when using a category scale in subjects with COPD, the perceived sense of effort in breathing during exercise is highly reproducible, correlates closely with physiologic measures defining the intensity of exercise, and is no more variable than physiologic parameters typically measured during an exercise test.