The distribution and elimination characteristics (Ke alpha, Ke beta, t1/2) of an intravenous bolus of biosynthetic IGF-I administered to 10 patients with Laron-type dwarfism (LTD, 3 children and 7 adults) and 6 healthy volunteers (3 children and 3 adults) are reported. The mean (+/- SD) endogenous level of IGF-I in the LTD patients was 5.24 +/- 2.77 nM/l and in the controls 27.2 +/- 9.4 nM/l. In the LTD patients the mean elimination constant (Ke beta) was 0.004 +/- 0.001 min-1 and t1/2 = 2.6 +/- 0.7 h, whereas in the controls, Ke beta was 0.003 +/- 0.009 min-1 and the t1/2 = 4.4 +/- 0.5 h (p less than 0.05). The more rapid elimination of injected IGF-I in the LTD patients is assumed to be due to the absence of the GH-dependent 150 kDa IGF-I binding protein.