To date, physical capacity of adults with GH deficiency (GHD) has been studied in terms of muscle strength, contractile properties and aerobic performance. As a result, scanty data are available regarding the maximum anaerobic performance of these patients with reference to healthy controls. Therefore, the objective of this study was to evaluate maximum anaerobic power of adults with GHD and of age-matched controls by two methods, one testing lactacid power (w.;(c)) through a 15-s-maximal bout on a bicycle ergometer, the other testing alactic power (w.;(j)) through a vertical jump on a force platform. Absolute w.;(c)and w.;(j)values were both found to be 35% lower(P<0.04) in GHD patients than in controls. Similarly, peak pedalling velocity (V(peak)) was 21% lower (P<0.04) in patients. When w.;(c)and w.;(j)were respectively normalized for thigh and lower limb muscle plus bone volumes and V(peak)for muscle length, differences between patients and controls were no longer significant. Furthermore, the rate of power loss during the cycling bout was approximately 35% in both groups. This observation was in line with similar delta (peak minus baseline) lactate capillary blood concentrations, being 6.3 mM/l in patients and 7.5 mM/l in controls (NS). Lactacid capacity, which represents the energy extracted from lactate metabolism, normalized for body mass was similar in the two groups. In conclusion, the maximum anaerobic power that can be developed by short-statured childhood-onset GHD adults is significantly lower in terms of absolute values, but not different from that of controls once appropriately normalized. Therefore, the changes in maximum anaerobic power of GH deficient patients seem to be a consequence of their smaller muscle mass.