Serial blood samples were collected from three dwarfFriesian foals to examine their endogenous growthhormone (GH) profiles, and the integrity of theGH-insulin-like growth factor-1 (IGF-1) axis wastested in one of them by examining its responses tothe administration of GH-releasing hormone (GHRH)and to 10 days of treatment with recombinant equineGH. The basal serum concentrations of IGF-1 inthe three dwarf foals were compared with those innine age-matched normal foals. All the dwarf foalssecreted endogenous GH. Stimulation with 7·0 μg/kgGHRH led to a 1400 per cent increase in plasma GHconcentration in the dwarf foal tested, and 10 dailysubcutaneous treatments with 20 μg/kg recombinantequine GH led to a 100 per cent increase in its serumIGF-1 concentration. The basal serum concentrationsof IGF-1 in the dwarf foals were not significantlydifferent from those of the normal foals.