A case of prolonged suxamethonium apnoea successfully terminated by the infusion of a commercial preparation of serumcholinesterase is reported. The patient appeared to be homozygous for the dibucaine resistant gene, having only 15% of normal activity in his serum. His dibucaine number was 21, and the Michaelis constant was 5.5 times that of normal sera. One and a half hours after receiving 110 mg suxamethonium for oesophagoscopy, the patient was still apnoeic with no response to ulnar nerve stimulation. Intravenous administration of 90 mg commercial serumcholinesterase, the equivalent to 1000 ml fresh human plasma, restored twitch and tetanic responses and the patient could lift his head 15 min after the beginning of the enzyme injection. The serumcholinesterase activity of the patient's serum increased by 55% (from 15% to 70%) following the injection. This rise was halved over the next 8 days.