Ten healthy subjects used to performing regular physical activity and eight subjects affected by idiopathic isolated GH deficiency (GHD) were enrolled; 22- and 20-kDa GH secretion and its biological activity were evaluated in response to pharmacological stimuli such as arginine, L-dopa or glucagon in GHD children, while the hormonal response to exercise was studied according to Bruce protocol in healthy subjects. We found a significant increase in 22- and 20-kDa GH level in healthy subjects after monitored physical exercise (MPE; basal 0.28 +/- 0.12 vs 7.37 +/- 2.08 ng/ml and basal 0.076 +/- 0.04 vs 0.116 +/- 0.05 ng/ml, respectively). Furthermore, the 22-kDa/20-kDa ratio significantly increased in children who had undergone MIRE and the GH bioactivity basal mean value also increased significantly after exercise (basal 2.86 +/- 0.76 vs 7.64 +/- 1.9 ng/ml). The mean value of 22-kDa GH in GHD patients increased significantly following GH pharmacological stimulation (2.78 +/- 0.63 ng/ml) when compared with mean basal (0.20 +/- 0.11 ng/ml) value. In the GHD group the basal concentration of 20-kDa GH significantly increased following GH pharmacological stimulation (0.34 +/- 0.11 vs 0.72 +/- 0.2 ng/ml); the 22-kDa/20-kDa ratio significantly increased too. Likewise, GH bioactivity in children with GHD increased significantly after pharmacological stimulation test (basal 2.53 +/- 0.56 vs 7.33 +/- 1.26 ng/ml). Both GH isoform concentrations and their biological activity are significantly increased in healthy subjects after submaximal exercise protocol and in GHD children after pharmacological stimuli.