The study described here investigates the influence of a specific alimentary Zn deficiency on the concentration of growth hormone (GH), insulin-like growth factor I (IGF-I) and insulin in the serum of force-fed rats. For this purpose 24 male Sprague-Dawley rats with an average bodyweight of 108 g were divided into 2 groups of 12 animals each. The Zn-deficient group and the control group received for 12 days a semi-synthetic casein diet with a Zn content of 1.3 and 25 ppm respectively. In order to prevent the reduced feed intake which occurs in Zn deficiency and the associated energy and protein shortage from interfering with the experimental parameters, all animals were fed 4 times daily by gastric tube. This made it possible to supply all animals with adequate-nutrients and to synchronise the feed intake exactly. After 12 days the depleted rats were in a severe state of Zn deficiency, as demonstrated by the reduction of Zn in the serum and the femur by 62% and 44% respectively and the 70% lower serum activity of alkaline phosphatase. In the Zn-deficient rats the concentration of GH in the serum was significantly increased by 78%, while IGF-1 and insulin were significantly reduced by 28% and 25% respectively. It is thought that the growth depression observed in the Zn-deficient rats in this study despite their identical feed intake is probably due to a reduced concentration of IGF-I and insulin and that the biological activity or the binding of GH to receptors is impaired in specific alimentary Zn deficiency.