GP130 is the shared receptor for members of the IL6 family of cytokines. Members of this family have been shown to enhance the survival of migratory(E10.5) or postmigratory (E12.5) murine primordial germ cells (PGCs) in culture; however, it is uncertain what role these cytokines play during PGC development in vivo. We have examined PGC numbers in E13.5 GP130-deficient mouse embryos and found that males exhibited a slight decrease in PGC numbers;females were normal. Also, we used the Cre-loxP system to inactive GP130 specifically in germ cells and found that this resulted in a fertility defect in females. These animals were found to have a slight reduction in the number of primary follicles and a major defect in ovulation. This data suggests that GP130 is required in female germ cells for their normal function, but is dispensable in male germ cells.