The Gene Expression Barcode is the first database to provide reliable absolute measures of expression for most annotated genes for human and mouse tissue types, including diseased tissue. The barcode algorithm is designed to estimate which genes are expressed and which are unexpressed in a given microarray hybridization. The output of our algorithm is a vector of ones and zeros denoting which genes are estimated to be expressed (ones) and unexpressed (zeros). We call this a gene expression barcode. Registration not required.