Two tests of stimulation: insulin + arginine and propranolol + glucagon were successively performed in 62 children who were either normal or had essential growth retardation. Average peak value was 10.6 +/- 1.1 ng/ml in the first test and 22.8 +/- 1.4 ng/ml in the second. In 56 cases the response obtained with propranolol + glucagon was higher than that obtained with insulin + arginine. Twenty-four false negative results were obtained employing insulin + arginine, stimulation by propranolol + glucagon resulting in normal values. The determination of the confidence interval at 95% and of the 3rd percentile did not allow to establish the lower threshold for the insulin + arginine test. For the propranolol + glucagon test 7.6 ng/ml for the interval at 95% and 8 ng/ml for 3rd percentile were found as minimal threshold. Therefore, a response below 8 ng/ml should be considered as pathological with the latter test.