The clinical course of alpha-chain disease in a Finnish boy is described. The disease presented with growth retardation and gastrointestinal symptoms at age 10 yr. Tests performed between the ages of 15 and 21 yr showed varying intestinal involvement including the large bowel, ileum, and distal jejunum. Alpha-chain disease protein was present in serum in fluctuating concentrations for at least 5 yr; it was produced by plasmacytoid cells found in the affected parts of the large bowel mucosa. The patient was treated with sulfasalazine and melphalan, but it is not clear that the clinical remission and the subsequent disappearance of the alpha-chain disease protein should be ascribed to this treatment. Concomitant with the normalization of the condition, a selective immunoglobulin A deficiency became apparent. The possibility is raised that an immunoglobulin A deficiency could have been the original defect in the patient, predisposing to intestinal infections; topical overstimulation of a defective immunoglobulin A system due to impaired mucosal defense might thus have explained the emergence of alpha-chain disease cells in the gut.