A study was made of the role of cytokine-induced neutrophil chemoattractant (CINC), regarded as a member of the interleukin-8 family, in rat experimental colitis induced by trinitrobenzene sulfonic acid and ethanol. Colonic myeloperoxidase (MPO) activity, a marker of tissue neutrophil infiltration, was observed to reach a plateau from 24 h to 1 week following the induction of colitis; tissue CINC levels, as measured by enzyme-linked immunosorbent assay, rose rapidly, peaking at 12 h before the rise in myeloperoxidase activity. The time-course of tissue leukotriene B4, another chemoattractant, was followed by that of MPO activity. Neutrophil accumulation into tissue in this model would thus appear to be under the control of CINC. Anti-CINC was also noted to inhibit 32.9 to 58.1% of chemotactic activity determined by bioassay during the same period, this being further evidence that CINC is a major chemotactic agent in this model. The present results indicate that CINC may have a crucial role in initiating neutrophil infiltration in experimental colitis.