miR2GO is a web-based platform for comparative analyses of human miRNA functions. It includes two programs: miRmut2GO and miRpair2GO. miRmut2GO implements a knowledge-based method to assess the functional effects of genetic and somatic mutations in microRNA seed regions. The functional effects of a mutation are analysed by semantic comparison of enriched gene ontology (GO) annotations of the target gene sets for the wild-type and mutated alleles. miRpair2GO compares the functions of two different miRNAs based on the enriched functional annotations of their target gene sets.