It has been suggested that growth hormone (GH) plays a role in the regulation of Factor VIII-von Willebrand factor complex and other parameters associated with haemostasis and vascular integrity. However, limited information is available on these features in GH-deficient patients. We therefore examined, in a double-blind, placebo-controlled crossover design, the effects of 4 months' replacement therapy with biosynthetic human GH in 22 GH-deficient adults on circulating haemostatic parameters and capillary fragility. A non-significant increase in the plasma levels of von Willebrand factor antigen (p = 0.09), Factor VIII antigen (p = 0.6), fibrinogen (p = 0.4) and fibronectin (p = 0.2) was observed at the end of the GH treatment period along with a non-significant decrease in tissue-type plasminogen activator (p = 0.2). Capillary fragility tended to decrease during GH therapy (p = 0.2). All variables remained within the reference range following both the placebo and the GH treatment period. It is concluded that GH-deficient patients display normal levels of the haemostasis parameters recorded, and that 4 months of GH therapy in a conventional replacement dose does not significantly affect these values.