Microarray technology and cell fractionation methods have been elegantly combined to enable the rapid identification of gene products that are likely to be secreted or associated with cell membranes (Nat. Genet. 25, 58–62, 2000). Secreted and membrane-bound proteins are particularly important as targets for drug development. Patrick Brown and his colleague isolated mRNA from cell membranes using established techniques, then used DNA microarrays to determine what genes were represented in the membrane-associated pool. By comparing this result to the DNA microarray analysis of non-membrane-associated mRNA from the same cells, they were able to determine the probability that a particular gene transcript would be membrane-associated (see inset). Their approach identified more than 275 human genes and 285 yeast genes encoding previously unknown secreted or membrane-associated proteins. Since microarrays can also be used to profile the expression patterns of genes, it should also be possible to determine which putative membrane-associated genes are turned on or off under different conditions.