Résumé : In order to study the influence of iron overload on the polymorphonuclear leucocyte (PMN) metabolism of patients on chronic hemodialysis, generation of superoxide anion (O2-) by PMN in whole blood was compared in two groups of hemodialyzed patients: group A consisted of twenty-one individuals with serum ferritin levels above 1000 ng/ml and group B of nineteen individuals with serum ferritin levels below 1000 ng/ml. Whereas basal production of O2- was similar in the two groups (6.3 +/- 4.6 vs 11.5 +/- 8.3 nmoles O2- 10(6) granulocytes-1 15 min-1) (mean +/- s.e.m.), PMN response to opsonized zymosan was significantly lower in group A as compared with group B (86.5 +/- 6.3 vs 120.4 +/- 8.2 nmoles O2- 10(6) granulocytes-1 15 min-1) (p less than 0.01). Superoxide anion generation induced by the dialysis procedure was reduced in eight patients from group A (89.2 +/- 32.1) as compared with eight patients from group B (374.3 +/- 100.0 nmoles O2- 10(6) granulocytes-1 15 min-1) (p less than 0.05). These data suggest that iron overload may be involved in the impairment of neutrophil phagocytosis in patients on chronic hemodialysis.