You know what they say: Gene regulators come in small packages (or, you know, something like that). In any event, microRNAs (miRNAs) are indeed both small and important regulators of gene expression, and microRNA.org is an online resource to explore the targets and expression patterns of this class of nucleic acids. MicroRNA.org is the brainchild of the Computational Biology Center at the Memorial Sloan-Kettering Cancer Center. It contains predicted target information for a large number of miRNAs in humans, mice, rats, Drosophila, and C. elegans. (In contrast, the experimentally observed miRNA expression patterns are only available for humans, mice, and rats.) Site visitors can download the data from the database. While a nice resource, microRNA.org is limited by the fact that it was last updated in 2010.