In an attempt to establish the reference ranges for lymphocyte subsets the distribution of lymphocyte-population-bearing surface markers such as CD3 (T cells), CD19 (B cells), CD4 (T helper/inducer cells), CD8 (T suppressor/cytotoxic cells), HLA-DR on CD3+ cells (activated T cells), and CD16 and/or CD56 on CD3- cells (NK cells) has been studied among normal male Saudi blood donors. Anticoagulated peripheral blood was stained with monoclonal antibodies and the lymphocytes were analyzed by flow cytometry for the expression of the above markers. Reference ranges were as follows: CD3+ (61 to 87%), CD19+ (5 to 27%), CD4+ (31 to 55%), CD8+ (24 to 56%), CD4+/CD8+ ratio (0.5 to 1.8), CD3+ HLA-DR+ (4 to 29%), and CD3- CD16+/CD56+ (4 to 29%). Furthermore, the absolute cell numbers for each lymphocyte subset are reported here for the first time for the Saudi male population. The most significant finding of the present study is the presence of a higher percentage and number of CD8+ T cells (P < 0.01) and a decreased CD4/CD8 ratio (P < 0.02) compared with the Caucasian controls. In addition, the Saudi male population has a significantly lower percentage and number of activated T cells (P < 0.05 and < 0.01, respectively) and a lower number of NK cells (P < 0.001).