We collected blood samples from 94 adult non-hematological outpatients and inpatients for complete blood count (CBC) without any flagging at Kaohsiung Medical College Hospital in order to investigate the effect of (1) different anticoagulants with Na2 EDTA vs K3 EDTA (2) the underfilling of blood collection volume (2 ml, 3. 5 ml vs standard 5 ml) (3) the difference in storage stability between 1 hour, 4 hours, 8 hours and 12 hours after venesection at room temperature on some selected hemogram parameters (WBC, RBC, hemoglobin, hematocrit, MCV, MCH, MCHC, platelet, percentage of neutrophil and lymphocyte). The automated hematology analyzer we used was SYSMEX NE-8000, (TOA, Japan). All the EDTA collection vacutainer tubes were supplied by Becton-Dickinson (New Jersey, U. S. A.) with the same lot number. Paired t- test was used for statistics. We found that values of hemoglobin, hematocrit, MCV and lymphocyte percentage collected in Na2 EDTA tubes were significantly higher than those collected in K3 EDTA (P < 0.05 for hemoglobin and lymphocyte percentage, and P all < 0.01 for others), while values of MCHC collected in Na2 EDTA were significantly lower than those collected in K3 EDTA (P < 0.05). For underfilling of blood sample, values of hematocrit and MCV with 2 ml blood volume were significantly lower than those with 5 ml blood volume (both P < 0.01), while values of MCHC with 2 ml blood volume were significantly higher than those with 5 ml blood volume (P < 0.01). When the collection blood volume was increased to 3.5 ml, there were no significant difference between values for 3.5 ml and 5ml blood volume (P all > 0.05). In the storage stability study, there was a significant sequential increase of hematocrit and MCV between 1 hour, 8 hours and 12 hours (P < 0.05 and < 0.01, respectively, for 8 hours, P all < 0.01 for 12 hours). There was also a significant sequential decrease of neutrophil percentage between 1 hour and 4, 8, 12 hours' storage at room temperature (P all < 0.01).