The behavior of HGH in basal conditions and after L-Dopa infusion was studied in a group of patients with diabetic retinopathy, in 9 obese and 8 control subjects. In both diabetics and obese subjects, increases found in HGH plasma levels after administration of the drug were slighter than in the controls. On the basis of these results it can be concluded that in diabetics the availability of energetic substrates may modify the HGH response to the L-Dopa stimulus. In obesity, the possibility is considered of a reversible defect in the sensitivity of the dopaminergic receptors, induced by metabolic and endocrine factors.