Recombinant human insulin-like growth factor I (rhIGF-I) was administered subcutaneously to 6 normal subjects and 2 patients with GH deficiency at a dose of 0.1 mg/kg for 7 consecutive days after breakfast. In normal subjects, plasma IGF-I levels increased from 217 +/- 22 ng/ml (Mean +/- SEM) to maximal levels of 581 +/- 6 ng/ml 4 h after the first administration of IGF-I. The blood glucose levels were statistically depressed 4 h after injection at 69 +/- 2 mg/dl. Similar plasma IGF-I and blood glucose profiles were observed after the seventh administration of IGF-I. The free form of IGF-I in plasma was 2.3 +/- 0.3 ng/ml in normal subjects and increased to maximal levels of 43.5 +/- 5.1 ng/ml 2 h after the first IGF-I administration. A similar pattern for the free form of IGF-I was observed after the seventh administration; however, the values obtained at 0, 1 and 2 h were greater after the seventh administration. In patients with G-deficiency, the plasma IGF-I and blood glucose profiles were similar to those observed in normal subjects, although the total IGF-I levels were low in these patients at all sampling points during the study. Slight decreases in serum insulin, uric acid, and creatinine were observed after the seventh administration of IGF-I. There were no changes in the excretion of urea nitrogen, creatine, creatinine, sodium, potassium, chlorine, calcium or C-peptide in the urine during the 7 days of IGF-I administration.