Using a modified version of the TLC/Salmonella assay developed by Bjorseth et al. (1982), 10 complex hazardous wastes were tested for mutagenic activity. The method couples thin layer chromatography (TLC) with the Salmonella/mammalian-microsome (Ames) assay for the detection of mutagenic constituents in complex mixtures. Crude hazardous wastes and selected hazardous waste extracts were fractionated on commercially available cellulose TLC plates. Mutagenicity testing was performed by applying a single overlay of minimal growth agar containing a tester strain of Salmonella and the optional metabolic activation system directly onto the developed chromatogram. Seven of 10 hazardous wastes demonstrated mutagenic activity when tested by the method. To assess the sensitivity of the modified TLC/Salmonella assay, 14 Salmonella mutagens from a wide range of chemical classes and polarities were tested. Eleven of the 14 mutagens were positive in the test system.