The aim of this study was to determine the effect of a 16-week intrahospital supervised, conditioning program including both resistance and aerobic type training on insulin-like growth factors 1 and 2 (IGF-1, IGF-2), several IGF-binding proteins (IGFBPs), and growth hormone (GH) in children receiving treatment against acute lymphoblastic leukemia (ALL). We also analyzed the effects of a 20-week detraining period on these hormones. Seven children (3 girls and 4 boys) aged 4-7 years in the maintenance phase of treatment against ALL performed 3 training sessions per week for 16 weeks of resistance (1 set of 8-15 repetitions of 11 exercises) and aerobic training (30 minutes at >or=50% heart rate max) followed by 20 weeks of detraining where no structured exercise program was performed. Levels of IFG-1 and IFG-2 did not significantly change after the intervention period or after the detraining phase. Likewise, levels of GH, IGFBP-2, and IGFBP-3 remained stable pre and posttraining and after the detraining period. IGFBP-1 levels significantly decreased after training (-43.8%, p = 0.014), whereas there were no significant differences between pretraining vs. detraining (-17.8%, p = 0.108) nor between posttraining vs. detraining (17.7%, p = 0.251). Exercise training did not have major effects on the IGFs, IGFBPs, and GH in children with ALL. Although the importance of these findings to long-term cancer prognosis and/or recurrence remains to be determined, the present data (particularly those on IGF-1 and IGFBP-3) support the idea that exercise training can be safely undergone during treatment against ALL with no major adverse effect.