The analysis of temporal patterns of gene expression in embryos is an essential component of any research program seeking to understand molecular mechanisms that control development. Little is known of early regulatory mechanisms that operate in primate oocytes and preimplantation-stage embryos. Such studies have been hindered by the cost of obtaining, and limited availability of, non-human primate oocytes and embryos, and by ethical and legal constraints on studies of human embryos. Over the past 4 years we have established the Primate Embryo Gene Expression Resource (PREGER) to circumvent these limitations. A set of over 200 samples of rhesus monkey oocytes and embryos has been converted to cDNA libraries, which are, in turn, used for a variety of molecular analyses. Both the libraries and cDNA dot blots can be distributed free of charge to anyone wishing to study gene expression at these stages. This includes providing an inexpensive and rapid method for confirming and extending results of gene discovery approaches such as microarray analysis. PREGER includes an on-line resource with a database and other useful tools for embryologists. The resource is being expanded to incorporate samples from other species and from embryonic stem cells.