With the near completion of the human genome project, reproductive biology is poised to enter the vastly more complex arena of proteomics. Proteomics involves the identification, characterization and quantitation of all proteins present in a cell at a particular metabolic state. Although the number of genes in the human genome is estimated to be about 27,000 +/- 5000, the number of proteins produced by humans is unknown, with estimates ranging as high as 1,500,000 distinct molecular entities. In order to address problems in the early stages of reproduction, proteomics must be scaled down to work with very few numbers of cells, termed zeptoproteomics. Mass spectrometry has rapidly become the key technology in proteomics, enabling rapid and facile identification and quantitation of femtomole and attomole quantities of a protein.