Résumé : Interleukin-6 (IL-6) was determined in serum and peritoneal dialysis effluent (PDE) of patients on chronic ambulatory peritoneal dialysis (CAPD) by a biological assay measuring the proliferation of the IL-6-dependent 7TD1 cell line. Six patients free of peritonitis displayed low but significant levels of IL-6 (mean +/- 42 pg/ml) in PDE, while IL-6 was undetectable in serum. In 6 patients with staphylococcal peritonitis, a tremendous increase in PDE levels of IL-6 was noted (range: 5,832-37,491 pg/ml), while serum IL-6 remained either undetectable or on a low level except in one case. After 5 days of antibiotic treatment, IL-6 levels in PDE returned to basal values. We conclude that CAPD results in an intraperitoneal secretion of IL-6 which is markedly but transiently increased during peritonitis episodes.