Animal studies have demonstrated that in addition to inhibiting growth hormone (GH) secretion octreotide inhibits in a direct manner hepatic or peripheral insulin-like growth factor I (IGF-I) generation. To test this hypothesis in humans we studied ten GH-deficient patients with frequent blood sampling during 38 h on two occasions. Regular GH therapy was discontinued 72 h prior to each study period. At the start of each study a subcutaneous (sc) injection of GH (3 IU/m2) was given (at 18.00 h). In a single-blinded crossover design, patients received a continuous sc infusion of either octerotide (200 μg/24 h) or placebo (saline). The pharmacokinetics of GH were similar on the two occasions. The area under the curve±sem of serum GH was 142.5±53.6 μg·l−1·h−1 (octreotide) and 144.8±41.8 μg·l−1·h−1 (placebo), (p=0.73); Cmax (μg/l) was 12.5±1.47 (octreotide) and 12.8±1.42 (placebo) (p=0.83), and Tmax (h) was 6.1±0.97 (octreotide) and 5.2±0.65 (placebo) (p=0.49). Growth hormone administration was associated with an increase in serum IGF-I (μg/l), which was identical during the two studies, from 85.3±19.4 to 174.25±30.3 for octreotide and from 97.0±26.4 to 158.8±28.2 for placebo. Mean IGF-I levels (μg/l) were 138.2±25.1 (octreotide) and 134.5±28.6 (placebo) (p=0.78). Similarly, the increase in IGF binding protein 3 (IGFBP-3) levels was identical. Mean IGFBP-3 levels (μg/l) were 2303±323 (octreotide) and 2200±361 (placebo) (p=0.25). Mean insulin levels were significantly lower during octreotide treatment (39.9±17.9 mU/l) than during placebo (59.7±17.8 mU/l) (p<0.05). Mean blood glucose levels were elevated significantly during octreotide infusion (5.98±0.23 mmol/l for octreotide and 5.07±0.16 mmol/l for placebo; p=0.001). Glucagon levels decreased non-significantly (p=0.07) and IGFBP-1 levels tended to increase during infusion of octreotide although not significantly (p=0.41). Levels of the lipid intermediates were identical on the two occasions. Alanine and lactate levels were significantly increased during octreotide infusion. Mean levels of blood alanine (μmol/l) were 470.8±24.2 (octreotide) and 360.1±17.8 (placebo) (p<0.02). Mean levels of blood lactate were 1038±81.0 (octreotide) and 894.4±73.8 (placebo) (p<0.04). We conclude that short-term continuous sc infusion of octreotide has no direct effect on the generation of IGF-I or the pharmacokinetics of exogenous GH in GH-deficient man.