Loss of physical performance is a universal problem of cancer patients undergoing chemotherapy. We postulated that this impairment can be partially prevented by aerobic exercise, In a randomized study, 33 cancer patients receiving high-dose chemotherapy followed by autologous peripheral blood stem cell transplantation (training group, T) performed an exercise program consisting of biking on an ergometer in the supine position after an interval-training pattern for 30 minutes daily during hospitalization, Patients in the control group (C, n = 37) did not train, Maximal physical performance was assessed with a treadmill test by admission and discharge. physical performance of the two groups was not different on admission, The decrement in performance during hospitalization was 27% greater in the central group than in the training group (P =.05); this resulted in a significantly higher maximal physical performance at discharge in the trained patients (P =.04), Duration of neutropenia (P =.01) and thrombopenia (P =.06), severity of diarrhea (P =.04), severity of pain (P =.01), and duration of hospitalization (P =.03) were reduced in ti-ts training group. We conclude that aerobic exercise can be safely carried out immediately after high-dose chemotherapy and can partially prevent loss of physical performance. Based on the potential significance of the observed outcomes, Further studies are warranted to confirm our results. (C) 1997 by The American Society of Hematology.