To further investigate the GH secretion in juvenile diabetics, blood glucose (BG) and plasma growth hormone (GH) were determined during controlled exercise performed in basal condition and under glucose infusion, in 7 controls and 22 juvenile diabetics aged 12-35 years, 10 of them with fundal vascular lesions. In controls, glucose infusion significantly lowered the exercise induced GH rise observed under basal conditions. In diabetics, under basal conditions, diabetics with low basal BG (BG < 100 mg/100 ml) had higher GH secretion than those with high basal BG (BG > 140 mg/100 ml; p < 0.05). Under glucose infusion, diabetics with normal BG peak values (not different from controls: BG = 284 ± (SD) 45 mg/l00 ml) had significantly higher plasma GH levels than controls (p < 0.01). In contrast, in diabetics with BG peak value higher than controls (BG > 374 ng/100 ml), plasma GH levels were not different from control values. This study indicates that exercise induced GH secretion in diabetics is mainly related to actual BG levels. Furthermore, we found no relation between the magnitude of GH secretion and the presence of retinopathy in diabetics.