The 24-h secretory pattern of hGH was studied by the aid of a continuous blood withdrawal pump in three Laron-type dwarfism (LTD) patients and compared with that in sex- and age-matched normal control subjects. It was found that the secretion of hGH was enhanced in the LTD patients, but in all three the diurnal secretory profile, as expressed by the number of pulses and the sleep-related maximal pulse, was preserved. In the younger LTD patients, women aged 19 and 21 years, the number of pulses was 9 and 7 (compared with 6 in the control subjects), the maximal hGH pulse amplitude was 164 and 280 ng/ml (compared with 135 ng/ml), the area under the curve (AUC) was 560 and 780 (compared with 268), and the average integrated concentration (A-IC) of hGH was 33.9 and 23.4 ng/ml (compared with 11.3). In the older LTD patient, a man aged 27 years, the hGH secretion was lower than that in the LTD women, but still higher than that in normal matched controls: the number of pulses was 4 (control 2), maximal pulse amplitude 67 ng/ml (control 19), AUC 231 (control 51), and A-IC 9.9 ng/ml (control 2.2). The decline in hGH secretion, which is characteristic of advancing age in normal subjects, seems to occur in LTD as well. Metabolic clearance rate (MCR) and production rate (PR) of hGH were measured in the 19-year-old female LTD patient. Her MCR was 73.4 ml/m2 per min, and her PR was 2,480 ng/ml compared with 158.3 and 839, respectively, in a normal subject. The exaggerated PR explains the elevation of plasma hGH in this syndrome and is probably the result of a lack of negative feedback due to insulin-like growth factor deficiency.