Mammalian preimplantation development is characterized by a number of major events. These potentially involve significant but transient changes in early embryonic gene expression. We have undertaken a meta-analysis of gene expression in mouse preimplantation development using a set of 71 346 expressed sequence tags (EST) derived from 15 non-normalized cDNA libraries. These libraries span seven stages of development from the unfertilized oocyte to the blastocyst stage. EST were clustered using UNIGENE: The 71 346 EST identified 11 483 separate genes, of which 1585 are not found elsewhere in the mouse. Aggregate sets of EST for each of the seven stages were analysed for differences in gene expression using Fisher's exact test. This analysis identified 109 genes that were differentially expressed. Some of these genes were associated with degradation of transcripts at the 1-cell stage whereas other genes underwent increased expression at the blastocyst stage. The set of 11 483 genes identified in mouse preimplantation embryo development provides the starting point for the design of DNA microarrays targeted at early mammalian embryogenesis. By anchoring the analysis of mouse preimplantation development in UniGene, it will be possible to identify homologous genes that are likely to be involved in human preimplantation embryo development.