Neutrophil's CL (CL-index) in were assayed in 18 patients with chronic lower tract infection (13 cases in the exacerbated phase and five cases in the stable phase) three times per case: before, during and after chemotherapy. Before the initiation of chemotherapy, the CL-index.N (neutrophil numbers x CL-index) in patients with exacerbation remained higher than in those without exacerbation. At the exacerbated phase, the CL-index of nine patients and the CL-index.N of 10 patients fell lower than those obtained before treatment. AT the stable phase, the CL-index and the CL-index.N did not change remarkably during and after chemotherapy.