Mutagenicity of 15 diaminodiphenylmethane and related compounds used or synthesized as epoxy resin hardner, many of which were 4, 4'-diamino-diphenyl derivatives, were examined by Ames preincubation assay using Salmonella typhimurium TA98 and TA100 in both absence and presence of metabolic activation system (S9 mix) . 8 compounds showed the mutagenicity in the presence of S9 mix.