A patient with macroamylasaemia in association with the acquired immunodeficiency syndrome is described. Patients with the acquired immunodeficiency syndrome commonly have gastrointestinal symptoms that often prompt serum amylase determination. Macroamylasaemia has been found to occur in a variety of diseases including various autoimmune disorders. The marked immunological abnormalities and increased circulating immunoglobulins associated with the acquired immunodeficiency syndrome may have predisposed this patient to macroamylase formation. Macroamylasaemia is a benign condition that requires no treatment and must be excluded in the patient with unexplained hyperamylasaemia to avoid unnecessary diagnostic tests and treatment.