beta(1C) and beta(1A) integrins are alternatively spliced variants of the human beta(1)-subunit; the former has been shown to inhibit cell proliferation, and the latter to promote it. Although some components of the beta(1) integrin subfamily are expressed in human endometrial and decidual cells during the menstrual cycle and early pregnancy, to date no information is available about the expression of beta(1C) integrin in endometrial and decidual tissues and its possible roles during implantation and pregnancy. To gain further insight on this subject, we have explored beta(1C) integrin expression in endometrial (proliferative, secretory, and atrophic) and decidual (from the first and third trimesters of pregnancy) tissue samples at both gene and protein levels by Northern and Western blotting analyses and by immunohistochemistry. beta(1A) protein levels were also measured in the same tissues as a control. The results of this study demonstrate that both beta(1C)- and beta(1A)-subunits are expressed in the endometrium and decidua. In the former, maximal beta(1C) expression was detected in atrophic endometria, whereas beta(1A) expression levels were increased in secretive and decreased in atrophic endometrial tissues compared with proliferative endometria. In addition, whereas beta(1A) levels were significantly increased in decidual tissues, compared with proliferative endometria, beta(1C) expression was dramatically reduced in the same tissues, thus pointing to selective down-regulation of beta(1C) expression in the decidua. These data suggest that the expression of beta(1C) integrin, a very efficient inhibitor of cell proliferation, may be modulated by the maternal microenvironment and may play a fundamental role in mediating trophoblast outgrowth and migration during pregnancy.