This paper presents the results of a case control study based on 55 patients identified with sclerosing peritoneal disease through the 1984 centre questionnaire. For each case with a confirmed finding of small bowel enclosed in a bag or 'cocoon' of thickened peritoneum, three controls were selected from the main EDTA Registry patient file. Questionnaires were sent out on cases and controls in order to compare exposure to a number of factors implicated in the aetiology of sclerosing peritoneal disease. These included a history of peritonitis, use of agents to sterilise the tubing connection, use of bacterial filters and buffers, drugs added to the dialysate, and history of medication with beta-blockers. Questionnaires were returned for 82% of cases and 74% of controls. Analysis of the returns using McNemar's test showed a significantly higher exposure to chlorhexidine in cases compared with controls. On the basis of this strong association, it seems advisable that the use of chlorhexidine to sterilise tubing connections for peritoneal dialysis patients should be halted.