Thirty-six nitrated furan and arenofuran derivatives were measured and quantitatively characterized by the T7 inactivation test. A wide range of substances previously studied allowed us to compare the collected quantitative data with those obtained by other workers using different short-term tests. Based on comparative statistical evaluation of these data a borderline was determined for the genotoxic effect: compounds having in our short-term test mutagenicity index (MI) values smaller than 8.0 are positive while the higher values represent negative genotoxicity. Classification of 36 nitrofuran/nitroarenofuran derivatives is given both on the basis of the quantitative genotoxicity scale and in terms of +/- on the qualitative scale. All but one compound were found to be genotoxic and the genotoxic activities of these compounds were compared with the results of other carcinogenicity or mutagenicity tests.