The pharmacokinetics and acute effects of an authentic recombinant DNA-derived human growth hormone (rhGH) produced by genetically engineered mammalian cells were determined in 12 healthy volunteers following intravenous (i.v.), intramuscular (i.m.) and subcutaneous (s.c.) administration of 4 IU (1.3 mg) hGH/m2 body surface area. Following i.v. administration, apparent elimination half-life of rhGH was 18 min. Following i.m. administration, a mean peak serum concentration of 36.9 ng/ml (range 13-61 ng/ml) occurred at 3 h, and following s.c. administration, more sustained but lower serum concentrations occurred, with mean peak concentrations of 16.4 and 16.3 ng/ml at 4 and 6 h (ranges 9.0-27.5 ng/ml and 6.5-35.5 ng/ml at 4 and 6 h, respectively). The mean area under the curves was lower after s.c. (134 +/- 48 ng.h.ml-1) than after i.m. (194 +/- 48 ng.h.ml-1) injections (p < 0.03). Comparable results were obtained for the same dose of rhGH given subcutaneously in concentrations of either 4 IU/ml or 10 IU/ml. Both i.m. and s.c. administrations caused similar increases in free fatty acids at 4 h and insulin-like growth factor I at 24 h. Insulin, C-peptide and blood glucose were almost unchanged during the first 4 h after administration, whereas leukocytes increased significantly (p < 0.0001). Local and systemic tolerance were good, and no adverse reactions were observed. In a GH-deficient child, hGH serum levels between 10 and 20 ng/ml were demonstrated for a period of 8 h after s.c. administration of 0.07 IU rhGH/kg body weight.