This is a brief overview on a series of studies performed in the Istituto Superiore di Sanità (Italian National Institute of Health), all focusing on the ability of mutagenicity short-term assays of identifying genotoxic agents and predicting carcinogenicity. The analytical tools of such studies were the multivariate data analysis statistical techniques. The overall picture points to three main classes of assays, on the basis of their responses to the chemical agents in the available data bases (mainly the comparative studies). The implications for practical chemical testing and battery design are discussed.