The present study was undertaken to examine the validity of using the OMNI scale of perceived exertion to regulate intensity during extended exercise periods. Forty-eight subjects (24 male, 24 female) were recruited and each subject completed a maximal graded exercise test (GXT) and two 20-min submaximal exercises. During the GXT, ratings of perceived exertion (RPE) as well as oxygen uptake (VO(2)) and heart rate (HR) equivalent to 50 and 70% of maximum VO(2) (VO(2max)) were estimated. During each submaximal exercise, subjects were instructed to produce and maintain a workload equivalent to the RPE estimated at 50 or 70% VO(2max), and VO(2) and HR were measured every 5 min throughout the exercise. Of the 48 subjects, 12 (6 male and 6 female) performed both the estimation and production trials on a treadmill (TM/TM), 12 (6 male and 6 female) performed both the estimation and production trials on a cycle ergometer (C/C), 12 (6 male and 6 female) performed the estimation trial on a treadmill and the production trial on a cycle ergometer (TM/C), and 12 (6 male and 6 female) performed the estimation trial on a cycle ergometer and the production trial on a treadmill (C/TM). No differences in VO(2) between the estimation and any 5 min of the production trial were observed at either intensity in TM/TM and C/C. No differences in HR between the estimation and any 5 min of the production trial were also observed at 50% VO(2max) in TM/TM and at both 50 and 70% VO(2max) in C/C. However, HR was higher at 20th min of the production trial at 70% VO(2max) in TM/TM. Both the VO(2) and HR were generally lower in TM/C and higher in C/TM. However, these differences diminished when values were normalized using VO(2max) of the same mode that other groups had attained. These data suggest that under both intra- and intermodal conditions, using the OMNI perceived exertion scale is effective not only in establishing the target intensity at the onset of exercise, but also in maintaining the intensity throughout a 20-min exercise session.