OBJECTIVE: The purpose of this study was to assess the efficacy of Borg's rating of perceived exertion (RPE) scale to predict maximal exercise levels to control exercise intensity in patients taking atenolol for the treatment of essential hypertension. Normally, a standard formula (220-age) is used for calculating a percentage of exercise intensity, but beta blockade can cause reductions in maximal heart rate of between 20 and 30%. METHODS: Patients were split into a control group-10 men and 10 women, aged 50 (SD 12) and 46 (9) respectively, who had risk factors for cardiovascular disease but were not taking any drugs, and a treatment group-11 men and 11 women, aged 53 (13) and 55 (13) respectively, who were established on 25-100 mg of atenolol. All patients performed two submaximal tests on a cycle ergometer. Test 1 was an estimation test, during which the RPE was reported for each increment in work rate. Test 2 was an RPE production test, during which the patient regulated the work rate according to his/her perception of effort at four predetermined points on the RPE scale (RPE 9, 13, 15, 17). RESULTS: In both tests the individual correlations (r) between RPE, heart rate, and work rate ranged from 0.96 to 0.99. Analysis of variance showed no significant difference in maximal heart rate and maximal power output for the control group when predicted from the regression lines of RPE versus heart rate and RPE versus power output in the estimation test. However, the prediction of maximal power output was lower in the women in the control group and patients in the treatment group when this was predicted from the effort production protocol (P < 0.01). When exercise intensity at each RPE was expressed relative to maximal power output there were no differences between treatment and control groups. CONCLUSION: The findings from this study confirmed the strong positive relation between RPE, heart rate, and work rate in these patients in both passive effort estimation and active effort production protocols. However, caution in applying these procedures is required because the prediction of maximal exercise levels may be lower when effort production procedures are used.