Over a six year period to 1985, 64 episodes of bacterial peritonitis in children on CAPD yielded 59 Gram-positive and 15 Gram-negative isolates. The former included 27 strains of Staphylococcus epidermidis (45.8%) and 24 Staph. aureus (40.7%). Staph. epidermidis is now the commonest cause of infection in these patients and like Staph. aureus is spread by leaks and disconnections. It is also more resistant to antibiotics than Staph. aureus and this causes problems in the choice of antibiotics with failure to control peritonitis and subsequent complications such as diminished efficacy of therapy, peritoneal adhesions, recourse to haemodialysis and superinfection with fungi. Both species showed 100% sensitivity to vancomycin, rifampicin and netilmicin. Other sensitivity figures for Staph. epidermidis were methicillin 52%, benzylpenicillin 15%, cefamandole 52%, cefotaxime 52%, amoxycillin-clavulanic acid 52%, gentamicin 63%, co-trimoxazole 48%, fusidic acid 59% and erythromycin 52%. Apart from benzylpenicillin (8%), Staph. aureus was much more sensitive, the figures being 96% for methicillin and 92-100% for the others. Our initial choice of 'best-guess' therapy early in the series was cefamandole with the addition of gentamicin or tobramycin for Gram-negatives. This is now inappropriate, based on relatively poor clinical results and increasing resistance to antibiotics, and we would now use vancomycin as first choice, with netilmicin added to cover Gram-negatives.