A highly increased peritoneal appearance rate of Il-8 was found in the acute phase that decreased to control values during recovery. A remarkable parallelism was observed for dialysate 11-8 and Il-6 with respect to the time course and the peritoneal appearance rate. In contrast, the appearance rate of TNFalpha was much less and had a different time course. In three of four cases where the dialysate Il-8 peak occurred on day 2, the dialysate Il-6 peak still coincided with 11-8, in contrast to TNFalpha (always day 1). Dialysate Il-8 generally exceeded serum concentrations during the entire follow-up, indicating intraperitoneal Il-8 synthesis. A positive correlation was present between the dialysate 11-8 peak and the maximal number of neutrophils in dialysate. This relationship was absent for Il-6 and TNFalpha. In five of six episodes where neutrophils were quantified on both day 1 and 2, the Il-8 peak occurred simultaneously with the neutrophil peak. These findings suggest that Il-8 is involved in the recruitment of neutrophils towards the dialysate during peritonitis.