The effects of withdrawal of ovarian hormones and absence of paternal antigens on numbers and distribution of cells expressing Ia, Thy 1.1 or leucocyte-common (LC) antigens in the rat metrial gland have been assessed. The distribution of these markers in non-pregnant uterus at various stages of the oestrous cycle has also been investigated. In primigravid rats at Day 15 of gestation, following ovariectomy on Day 12, marker distribution was not different from that in uninterrupted pregnancy. However, there was a significant increase in the percentage of cells expressing LC antigen, which was not accompanied by an increase in the percentage of the glycoprotein-containing, LC antigen-positive granulated metrial gland (GMG) cells. It was suggested that the accumulation of LC antigen-positive, non-GMG cells might represent the precursors of GMG cells. In deciduomata-bearing rats, there was a significantly lower percentage of LC antigen-bearing cells at Day 13 of pseudopregnancy than in pregnant rats at Day 13, but no difference in the percentages of GMG cells was noted. Cells expressing Ia, LC or Thy 1.1 antigens were detected in the endometrial stroma, surrounding endometrial glands and the luminal epithelium of the non-pregnant uterus.