Published reports on the possible changes in the various immune cell populations, especially the total lymphocyte and CD4 cell counts, during the menstrual cycle in Nigerian female subjects are relatively scarce. The aim of the present study was therefore to determine possible changes in the total and differential white blood cell [WBC] counts, total lymphocyte count [TLC] and CD4 cell count during the menstrual cycle in apparently healthy reproductive aged female undergraduate students in Port Harcourt, Nigeria. A total of 61 apparently healthy HIV sero-negative female undergraduate students of the University of Port Harcourt, Nigeria aged between 17 and 30 years, were recruited into the study. Subjects were allowed their normal daily routines but restricted from excessive physical activities for the duration of the study. After a menstrual history, blood was collected from each subject at the different phases of the menstrual cycle: menstrual, follicular, ovulatory and luteal. Total WBC and differential counts were determined manually; TLC was obtained by multiplying the percentage lymphocytes by the total WBC count; CD4 cell counts were determined by flow cytometry. Single factor analysis of variance showed significant differences only in the values of total WBC, and differential neutrophils, lymphocytes, and eosinophil counts [p<0.05]; no significant differences were observed in the values of monocytes, basophils, TLC and CD4 cell count during the phases of the menstrual cycle. The present study confirms previous reports of significant physiological variations in the leukocyte counts during the phases of the normal menstrual cycle. However, our results suggest that apparently TLC and CD4 cell count do not undergo a similar physiological variation.