Background:Most studies on blood donors are centered on the selective evaluation of red blood cell parameters with little or no regard to white blood cells and platelets.Methods:One hundred and twelve male blood donors comprising 43 first-time and 69 regular blood donors, drawn from a tertiary health facility in the Niger Delta of Nigeria, participated in the study. Their hematological parameters were assessed using a 3-part differential autohematology analyzer (PCE-210 N).Results:Of the blood donors, 18.8% were found to be anemic (packed cell volume [PCV] <33%) while 12.5% were leukopenic (white blood cell [WBC] count <2.0 × 109/L). The leukopenia observed in this study was largely due to the significant reductions in both the absolute lymphocyte (P = 0.019), percent lymphocyte (P = 0.016), and percent monocyte count (P = 0.008). Anemia was obviously due to the reduction in the red blood cell (RBC) count, PCV, hemoglobin (Hb), mean cell Hb (MCH), and red cell distribution width (RDW) values. Significant positive correlations were found between PCV and total WBC count (r = 0.309; P < 0.01) while a negative correlation was found between PCV and absolute lymphocyte counts (r = −0.191; P < 0.005) and RDW (r = −0.219; P < 0.05). Comparison of the mean values of the first-time versus regular blood donor parameters revealed that six parameters were significantly reduced in the regular blood donors (PCV, absolute WBC count, percent monocytes, RBC count, Hb, PCV). The reference ranges of hematological parameters for Port Harcourt donors are also presented in this study. No thrombocytopenia was observed.Conclusion:Regular blood donation not only affects red cell parameters but also those of white cells. Subclinical leukopenia is present among regular blood donors in this locality. First-time blood donors would be most preferable when the concentrated white blood cell component of blood needs to be prepared.