The effects of dl-propranolol, d-propranolol, butoxamine or practolol on erythropoietin (ESF) production in rabbits exposed to hypoxia (0.42 atmosphere) for 18 hours were investigated. Rabbits treated with dl-propranolol (4 or 8 mg/kg i.p.) or butoxamine (15 or 30 mg/kg i.p.) produced significantly less ESF in response to hypoxia than did saline-treated control animals. ESF production in rabbits given d-propranolol or practolol during hypoxia was not significantly different from that of control animals exposed to hypoxia. Based on the proposed selectivity of butoxamine for beta2 adrenergic receptors and of practolol for beta1 adrenergic receptors, it is suggested that ESF production in rabbits exposed to hypoxia may involve the activation of beta2 adrenergic receptors.