Approximately 15 percent of couples experience infertility, yet no abnormalities can be detected in the man or the woman. In a number of couples, their embryos unexpectedly slow down growth or stop growth completely. Some of these situations may be genetically determined. For instance, a portion of cases may be caused by poor egg quality related to genetic or functional deficiencies in heretofore unidentified human maternal effect genes. A model has been developed of such unexplained fertility by creating a mouse line lacking a critical maternal effect gene. (Maternal effect genes produce mRNA or proteins that accumulate in the egg and are required for normal early embryonic development.) This pilot project will test the hypothesis that a similar defect may be a cause of human infertility.