Cervical ripening during parturition is associated with rapid production of catabolic enzymes by invading leukocytes and increased collagen metabolism. The recruitment of leukocytes is regulated by various factors including inflammatory mediators, prostaglandins and matrix metalloproteinases. Sex steroids may be indirectly or directly involved in this process. This study aimed to evaluate the expression of oestrogen receptor beta (ER beta) in blood cells infiltrating the cervix during pregnancy and parturition. Cervical biopsies were obtained from term pregnant, post-partal and non-pregnant women. The ER beta protein and leukocyte markers CD45 and CD68 were evaluated by single and double labelling immunohistochemistry. Quantitative values were assessed using a microscope and a high-resolution camera connected to a computer with image analysis program. The number of CD45(+) and CD68(+) cells in the cervix increased in term pregnancy and post-partum compared with the non-pregnant state. The ER beta antigen was co-localized with CD45 leukocyte common antigen and CD68 macrophage specific antigen in blood leukocytes infiltrating the cervical tissue. The presence of ER beta in the cervical leukocytes suggests that oestrogen may directly regulate leukocyte functions in the cervix.