In intravesical therapy for superficial bladder carcinoma urothelial cells may, through the production of cytokines, contribute to the bacillus Calmette-Guerin (BCG)-induced local immunological reaction and associated antitumor efficacy. The aim of this study was to investigate such a role for the neutrophil-attracting cytokine interleukin-8 (IL-8). The appearance of IL-8 in patients urine after BCG therapy was compared with BCG-induced IL-6 and IL-2 and the stability of IL-8 in urine was tested. Compared to IL-6 and IL-2, a rapid induction of IL-8 was observed, occurring after the first BCG instillation. Urinary IL-8 was highly stable, even after 24 h incubation at 37 degrees C. The IL-8 concentration after the first instillation seemed to be associated with subsequent development of an immune response. Consequently, IL-8 seems an attractive candidate for investigation of its prognostic value for a clinical response to BCG therapy.