Lactoferrin, an iron-binding glycoprotein, kills bacteria and modulates inflammatory and immune responses. Presence of lactoferrin in the female reproductive tract suggests that the protein may be part of the mucosal immune system and act as the first line of defense against pathogenic organisms. We have discovered that lactoferrin is a major estrogen-inducible protein in the uterus of immature mice and is up-regulated by physiological levels of estrogen during proestrous in mature mice. In the present study, we examined lactoferrin gene expression and its response to estrogen stimulation in the female reproductive tract of several strains of immature mouse, rat, and hamster. The lactoferrin expression in the cycling adult female rat was also evaluated. Lactoferrin gene polymorphism exists among the different mouse strains. In the three inbred mouse strains studied, lactoferrin gene expression is stimulated by estrogen in the immature uterus, although it is less robust than in the outbred CD-1 mouse. We found that the lactoferrin gene is constitutively expressed in the epithelium of the vagina and the isthmus oviduct; however, it is estrogen inducible in the uterus of immature mice and rats. Furthermore, lactoferrin is elevated in the uterine epithelium of the mature rat during the proestrous and estrous stages of the estrous cycle. Estrogen stimulation of lactoferrin gene expression in the reproductive tract of an immature hamster is limited to the vaginal epithelium. The present study demonstrates differential expression and estrogen responsiveness of the lactoferrin gene in different regions of the female rodent reproductive tract and variation among the rodent species studied.