Nine patients with an unusual and serious intraabdominal complication of the beta-adrenergic blocking agent practolol seen since 1973 are reported. The striking and bizarre peritoneal changes induced by the drug have distinctive features that are not shown by other forms of peritoneal disease. The cases presented with small bowel obstruction, usually chronic in type and often associated with profound weight loss and an abdominal mass. Characteristic radiological features were present. The abnormalities at laparotomy were impressive, with a gross proliferation of the visceral peritoneum which formed a dense white cocoon which encased, constricted and markedly shortened the small bowel, usually from the duodenojejunal flexure to the ileocaecal valve. The obstruction was relieved by mobilizing the small bowel from the ensheathing tissue. Restoration of alimentary function after surgery was delayed but the long term result was satisfactory with full relief of symptoms and the absence of recurrent obstruction during the follow-up period. This complication may arise after treatment with the drug has been stopped, and although long term oral therapy has been discontinued, further cases will almost certainly present for some time to come.