We investigated the clinically allowable error for laboratory quality control of blood cell count in Japan. We have asked 409 members of Japanese Association of Clinical Hematology for an appropriate clinical allowance on the values of red blood cell count (RBC), hemoglobin value (Hb), mean corpuscular volume (MCV), white blood cell count (WBC) and platelet count (PLT). We delivered the lists in which 5 different allowable errors (2, 3, 5, 10 and 20%) were indicated on each blood cell count so that each member could check one of them. The data were collected within a month and were analyzed with computer. The results showed that 312 (76.3%) members choose 3 or 5% as an allowable error for RBC, 393 (96.1%) selected 2, 3 or 5% for Hb, 314 (76.8%) choose 3 or 5% for MCV, 358 (77.5%) indicated 3, 5 or 10% for WBC and 294 (72.6%) selected 5 or 10% for PLT. Based on these data, we propose the following clinical allowances for the values of blood cell count; 4% for RBC, 3% for Hb, 4% for MCV, 5% for WBC and 7% for PLT.