The mutagenic potential of seven mild gasification products was examined, using the preincubation variant of the Salmonella assay. The mild gasification products tested included two full boiling range liquids, a solid brittle residue, a coal-tar, two composite materials having a liquid/tar consistency (L/T-composite), and a composite coal-tar. The products were tested for mutagenicity using Salmonella-typhimurium TA-98, TA-100, and YG1024 as the tester strains in the presence or absence of an S9 system. The substances were tested at concentrations of up to 400 micrograms (microg) per plate using dimethyl-sulfoxide (DMSO) as the solvent and up to 2,000microg/plate using Tween-80 as the solvent. Only the two full boiling range liquids and the composite coal-tar showed significant mutagenic activity in strains TA-98 and YG1024 in the presence of S9 mix. The mutagenic response was greater in YG1024 than in TA-98. The mutagenicity of the full boiling liquids was greater when tested in Tween-80. The mutagenicity of the coal-tar composite was greater in DMSO than in Tween-80. One of the L/T-composites was separated into the liquid and tar phases and tested for mutagenicity in strains TA-98 and YG1024 using DMSO as the solvent. Mutagenic activity was detected in the tar phase, but not in the liquid phase or in the whole sample. The authors conclude that the mutagenic activity detected in some of the gasification products is probably due to higher molecular weight components in the materials. Some of the mutagenic components may be aromatic amines, as manifested by the greater responses occurring in YG1024, a strain with enhanced sensitivity to aromatic amines and nitroarenes compared to TA-98.