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The influence of peripherally administered adrenaline on the secretion of human growth hormone (HGH) and cortisol was investigated in 14 normal subjects. In a control group, HGH and cortisol release was stimulated by insulin infusion for 30 min (0.1 IU/kg). This procedure was compared with a similar insulin infusion which was started 60 min after initiating an adrenaline infusion for 150 min (6 μg/min). Adrenaline did not significantly alter the basal levels of HGH and cortisol. The mean maximal HGH rise during insulin hypoglycaemia (38.9 ± 7.2 ng/ml) was significantly (P < 0.005) inhibited by simultaneously administered adrenaline (9.6 ± 3.0 ng/ml). The same action of adrenaline was also found to be effective on cortisol release. The rise in plasma cortisol after insulin infusion (16.0±1.4 μg/100ml) was suppressed by adrenaline to 6.4 ± 2.2μg/100 ml (P < 0.005). Blood glucose and plasma free fatty acids (FFA), increased by adrenaline administration, were decreased significantly after insulin infusion. These results suggest an inhibitory effect of peripheral adrenaline on insulin-induced secretion of HGH. Blood glucose and plasma FFA levels seem to have no effect on this action. Whether there is a negative feedback between HGH and adrenaline should be considered. It is possible that the inhibition of cortisol release by adrenaline is mediated by an inhibiting effect on ACTH release, in the same manner as on the release of HGH.