Impaired cardiorespiratory fitness is associated with inferior survival in patients preparing to undergo hematopoietic cell transplantation (HCT). Exercise training based on short, higher intensity intervals has the potential to efficiently improve cardiorespiratory fitness. We studied home-based interval exercise training (IET) in 40 patients before autologous (N=20) or allogeneic (N=20) HCT. Each session consisted of five, 3 min intervals of walking, jogging or cycling at 65-95% maximal heart rate (MHR) with 3 min of low-intensity exercise (<65% MHR) between intervals. Participants were asked to perform sessions at least three times weekly. The duration of the intervention was at least 6 weeks, depending on each patient's scheduled transplantation date. Cardiorespiratory fitness was assessed from a peak oxygen consumption test (VO2peak) and a 6 min walk (6MWD) before and after the intervention period. For the autologous HCT cohort, improvements in VO2peak (P=0.12) and 6MWD (P=0.19) were not statistically significant. For the allogeneic cohort, the median VO2peak improvement was 3.7 ml/kg min (P=0.005) and the median 6MWD improvement was 34 m (P=0.006). Home-based IET can be performed before HCT and has the potential to improve cardiorespiratory fitness.