The investigation of peripheral blood lymphocyte (PBL) subpopulations is of interest in a wide variety of inflammatory diseases. Since the number of circulating lymphocytes has been shown to be affected by smoking habits, it seems useful to know how PBL subpopulations are influenced. We therefore determined percentages and absolute numbers of a wide range of PBL subpopulations in smokers (n = 14) and nonsmokers (n = 14). PBLs were obtained from healthy volunteers and analyzed by flow cytometry using antibodies for the detection of CD3, CD4, CD8, CD19, CD56, CD57, CD45RO, CD45RA, alpha/beta and gamma/delta T cell receptor epitopes. With the exception of CD3+ cells, no differences between smokers and nonsmokers were found regarding percentages of PBL subpopulations. Smokers were found to have higher absolute numbers of PBLs in the following subpopulations compared with nonsmokers: CD3+, CD4+, CD3+ alpha/beta +, CD45RO+/CD4+, and CD45RA+/CD4+. Cytotoxic lymphocytes, natural killer cells, and B cells did not differ in number between smokers and nonsmokers. There was likewise no difference in the number of the CD8+ alpha/beta + and all cells bearing the gamma/delta T cell receptor. Smoking increased the number of T cells and mainly CD4+ PBLs. The smoking habits of healthy control groups should therefore be taken into account when comparing lymphocyte subpopulations in different diseases.