Exercise intolerance is common in hemodialysis (HD) and renal transplant (RTx) patients. Aim of the study was to assess to what extent exercise capacity and skeletal muscle strength of RTx patients differ from HD patients and healthy controls and to elucidate potential determinants of exercise capacity in RTx patients. Exercise capacity, muscle strength, lean body mass (LBM) and physical activity level (PAL) were measured by cycle-ergometry, isokinetic dynamometry, DEXA and Baecke Questionnaire, respectively, in 35 RTx, 16 HD and 21 controls. VO(2)peak and muscle strength of the RTx patients were significantly lower compared to controls (p < 0.01), but not different compared to HD patients. In RTx patients, strength (p < 0.001), PAL (p = 0.001) and age (p = 0.045) were significant predictors of VO(2)peak. Muscle strength was related to LBM (p = 0.001) and age (p = 0.001), whereas gender (p < 0.001) and renal function (p = 0.01) turned out to be significant predictors of LBM. No effects of corticosteroids were observed. Exercise capacity and muscle strength seem equally reduced in RTx and HD patients compared to controls. In RTx patients, muscle strength and PAL are highly related to exercise capacity. Renal function appears to be a significant predictor of LBM, and through the LBM, of muscle strength and exercise capacity.