In children with cystic fibrosis, objective parameters of exercise tolerance are needed which are easy to measure in nonspecialized centres. We investigated maximal workload (W'max) in children with cystic fibrosis in relation to body weight and fat-free mass, and compared this with results for maximal oxygen consumption (V'O2,max). Fourteen patients with cystic fibrosis performed an incremental maximal exercise test on a bicycle ergometer. W'max, V'O2,max, body weight and fat-free mass were measured. W'max and V'O2,max were significantly correlated (r = 0.91; p < 0.001). Using standard deviation scores in relation to reference values, W'max and V'O2,max per kilogram body weight were significantly higher than uncorrected W'max and V'O2,max (mean difference (95% CI) 0.63 (0.24-1.01) and 0.91 (0.32-1.49) SD units, respectively). There was no such difference after correction for fat-free mass. Standardized V'O2,max was significantly higher than standardized W'max (mean difference (95% CI): 1.59 (1.14-2.04)), also after correction for body weight and fat-free mass. In children with mild-to-moderate cystic fibrosis, maximal workload per kilogram fat-free mass, but not per kilogram body weight, is a useful parameter to correct for diminished nutritional status. In these patients, maximal workload is consistently lower than maximal oxygen consumption. Taking into account this difference, maximal workload and maximal workload per kilogram fat-free mass can be used for follow-up of paediatric patients with cystic fibrosis in nonspecialized settings.