The concentrations of dexamethasone and prednisolone in the plasma of pigeons are measured by radioimmunoassay. The plasma curves show a more rapid ascent and steeper descent after dexamethasone injection (1 mg, 2 mg, 4 mg and 10 mg/kg of body weight IM) than after prednisolone injection (3 mg, 5 mg, 10 mg and 50 mg/kg of body weight IM). The longer-lasting effect after prednisolone injection could likewise be seen in the white blood count. The immunosuppressive effect of glucocorticoid preparations especially should be considered when applying antibiotics.