The present comparative evaluation aims at establishing whether the basic structure of dialysis membrane is able to predict long-term clinical outcome. From a population of 1,256 patients on renal dialysis treatment, treated by the Institute of Nephrology and Dialysis of the St. Orsola University Hospital of Bologna from 1963 to 1993, 122 patients were retrospectively selected for the present study. Patients were divided into two different groups according to the kind of dialysis membrane used--cellulose-based (64 patients) and synthetic-based (58 patients) membranes. The parameters considered were: intradialytic biology, long-term biocompatibility, survival and morbidity, and cost/benefit. The results obtained demonstrate that cellulosic membranes can be said to cause a greater acute intradialytic biological response than synthetics, though not to a significant degree. There are, however, no significant differences in the biological changes from group to group. Nonsignificant differences were noted in long-term survival general morbidity. In terms of sheer cost, synthetic membrane treatment is anything up to 200% dearer than cellulosic.