The expression of three different members of the gap junction multigene family, alpha 1 (Cx43), beta 1 (Cx32), and beta 2 (Cx26), was analysed in the rat implantation chamber (a structural unit containing fetal, extraembryonic and maternal components within the pregnant uterus) during mid- and late stages of gestation as well as in the delivering, post-partum and non-pregnant uterus. A differential, spatiotemporal and cell-type-specific regulation of gap junctional coexpression was observed for beta 1 and beta 2 in all epithelia examined (visceral, luminal and glandular), as well as for alpha 1 and beta 2 in decidual cells and keratinocytes of the fetal epidermis. alpha 1 antigen was detected in the mesometrial stroma, mesometrial myometrium, connective tissue, mesothelia of the amnion and visceral yolk sac and in the allantoic mesodermal layer throughout gestation. In addition, expression of alpha 1 in the placental basal zone and trophoblast giant cells coincided with the differentiation of these cells. beta 2 expression was observed prominently in the chorionic villi of the placental labyrinth. The presence of beta 1 and beta 2 in the visceral epithelium (visceral yolk sac = the primary route for embryonic nourishment prior to the formation of the chorioallantoic placenta) and beta 2 in the chorionic villi (placental barrier = the major fetomaternal exchange route) suggests that gap junctions have an important role in fetomaternal communication.