To study the significance of biofilm bacteria in CAPD peritonitis, in a preliminary study, we compared the growth of planktonic and biofilm bacteria by parallel cultures of the same PD effluent in 14 patients with CAPD-associated peritonitis. Planktonic bacteria were isolated by routine microbiologic culture techniques and biofilm bacteria by the use of a modified Robbins' device (MRD). Antibiotic sensitivity or MIC's of bacterial strains isolated by the two techniques were compared. This comparison of the IC identified a subgroup of patients who developed recurrent antibiotic resistant biofilm-induced peritonitis and their peritoneal catheters were subsequently removed.