ReMark is a fully automatic tool for clustering orthologs by combining a Recursive and a Markov clustering (MCL) algorithms. The ReMark detects and recursively clusters ortholog pairs through reciprocal BLAST best hits between multiple genomes running software program (RecursiveClustering.java) in the first step. Then, it employs MCL algorithm to compute the clusters (score matrices generated from the previous step) and refines the clusters by adjusting an inflation factor running software program (MarkovClustering.java). This method has two key features. One utilizes, to get more reliable results, the diagonal scores in the matrix of the initial ortholog clusters. Another clusters orthologs flexibly through being controlled naturally by MCL with a selected inflation factor. Users can therefore select the fitting state of orthologous protein clusters by regulating the inflation factor according to their research interests.