BACKGROUND: We evaluated the analytical performance of LC-175CRP TM (Horiba Ltd., Kyoto, Japan), an automated blood cell counter and C-reactive protein (CRP) measuring instrument, and its clinical usefulness. METHODS: LC-175CRP was evaluated for linearity, precision, and comparison using patient specimens and quality control material. Usefulness of simultaneous measurement of WBC count and CRP was analyzed using results from 114 patients with infectious or inflammatory diseases. RESULTS: LC-175CRP showed a good linearity (R(2) > or =0.98, P<0.001) and within-run and total-run CVs within 8% for all items analysed. Good correlations were found for all analyzed parameters (r > or = 0.94, P<0.001) except monocyte proportion (r=0.35, P=0.02). Among the 55 patients who showed abnormal results of either WBC or CRP, 48 patients (87.3%) showed CRP elevation alone. CONCLUSIONS: LC-175CRP is a small instrument and easy to operate, offers simultaneous, rapid measurement of blood cell count and CRP, and shows an excellent performance. It can be very useful at the emergency room or physician's office for patients suspected to have acute infections or inflammations.