MicroRNA.org is a comprehensive resource for microRNA target predictions and expression profiles. It uses the miRanda algorithm, which incorporates biological knowledge and an updated compendium of mammalian microRNAs to predict targets. Expression profiles are derived from sequencing data of various tissues and cell lines. The site provides a user-friendly interface to explore target genes, microRNA cooperativity, and expression in different tissues. The database is designed for flexibility to incorporate new discoveries. The resource offers functional information about microRNAs and their interactions in various species, aiding in novel discoveries of microRNA regulation. MicroRNAs regulate gene expression by binding to mRNAs, primarily in the 3'-UTR. Target recognition involves base-pairing, with the 5' end (seed region) being crucial. The miRanda algorithm calculates optimal sequence complementarity using a weighted dynamic programming approach. It also considers sequence conservation and uses the PhastCons score for conservation filtering. The site includes data from MirBase, UCSC genome browser, and other sources for microRNA sequences and expression. The microRNA.org database is organized in MySQL relational databases and uses Java, Struts, JSPs, and JavaScript for implementation. Users can explore target predictions, expression profiles, and link microRNAs to their target genes. The site provides downloadable data and source code. It addresses common questions about microRNA regulation and expression, such as target genes, microRNA targets, and expression in specific tissues. Future extensions include adding microRNA data for other organisms and integrating experimental data with pathway information. The site aims to incorporate new findings and improve prediction algorithms. It also plans to link experimental data with pathway resources. The resource is supported by grants and acknowledges contributions from various researchers. The study highlights the importance of microRNAs in various biological processes and their role in disease.MicroRNA.org is a comprehensive resource for microRNA target predictions and expression profiles. It uses the miRanda algorithm, which incorporates biological knowledge and an updated compendium of mammalian microRNAs to predict targets. Expression profiles are derived from sequencing data of various tissues and cell lines. The site provides a user-friendly interface to explore target genes, microRNA cooperativity, and expression in different tissues. The database is designed for flexibility to incorporate new discoveries. The resource offers functional information about microRNAs and their interactions in various species, aiding in novel discoveries of microRNA regulation. MicroRNAs regulate gene expression by binding to mRNAs, primarily in the 3'-UTR. Target recognition involves base-pairing, with the 5' end (seed region) being crucial. The miRanda algorithm calculates optimal sequence complementarity using a weighted dynamic programming approach. It also considers sequence conservation and uses the PhastCons score for conservation filtering. The site includes data from MirBase, UCSC genome browser, and other sources for microRNA sequences and expression. The microRNA.org database is organized in MySQL relational databases and uses Java, Struts, JSPs, and JavaScript for implementation. Users can explore target predictions, expression profiles, and link microRNAs to their target genes. The site provides downloadable data and source code. It addresses common questions about microRNA regulation and expression, such as target genes, microRNA targets, and expression in specific tissues. Future extensions include adding microRNA data for other organisms and integrating experimental data with pathway information. The site aims to incorporate new findings and improve prediction algorithms. It also plans to link experimental data with pathway resources. The resource is supported by grants and acknowledges contributions from various researchers. The study highlights the importance of microRNAs in various biological processes and their role in disease.