A 69-yr-old man, who was concurrently being treated with pilocarpine nitrate and timolol malcate eye drops, developed a bradycardia and became hypotensive during halothane anaesthesia. Both timolol and pilocarpine were subsequently identified in a 24-h collection of urine. Timolol (but not pilocarpine) wai detected in a sample of plasma removed during surgery; the plasma concentration of timolol (2.6 ng ml−1) was consistent with partial β-adrenoceptor blockade. It is postulated that this action may have been enhanced during halothane anaesthesia with resultant bradycardia and hypotension. Pilocarpine may have had a contributory effect.