Leukocyte subsets were detected by immunohistochemical methods in cervical tissue in either the first trimester or at term pregnancy. In tissue obtained during first trimester lower total numbers of leukocytes were observed in comparison with late pregnancy (2.7 cells/0.04 mm2 versus 5.5 cells/0.04 mm2). The major subgroup of leukocytes present in early pregnancy was T-lymphocytes. The majority of these cells were of the suppressor/cytotoxic subtype. Neutrophils were present at about 1/5th of the density of T-lymphocytes. Very few macrophages were observed at this stage. At term pregnancy, neutrophils were present in significantly higher numbers than during first trimester with no difference between tissue obtained before or during active labour. Macrophages were present at about 10-fold higher density than during early pregnancy. In conclusion, tissue-bound leukocytes are present in the human cervix at a higher density in late pregnancy compared to first trimester. The increased densities of neutrophils and macrophages at this stage indicate a role for these cells during cervical ripening.