TOPAL 2.0: improved detection of mosaic sequences within multiple alignments. MOTIVATION: The Dss statistic was proposed by McGuire et al. (Mol. Biol. Evol., 14, 1125-1131, 1997) for scanning data sets for the presence of recombination, an important step in some phylogenetic analyses. The statistic, however, could not distinguish well between among-site rate variation and recombination, and had no statistical test for significant values. This paper addresses these shortfalls. RESULTS: A modification to the Dss statistic is proposed which accounts for rate variation to a large extent. A statistical test, based on parametric bootstrapping, is also suggested. AVAILABILITY: The TOPAL package (version 2) may be accessed from http:/ / and by anonymous ftp from typ:// in the directory pub/phylogeny/topal.