Novel pitches produced by N-methylpyrrolidone (NMP) extraction of coal were evaluated for their biological reactivity in the following bioassays : Salmonella reversion or mutation assay, V79 cell micronucleus assay, medaka larval survival assay, and cytochrome P4501A1 induction, as reflected by ethoxyresorufin O-deethylase activity. The potential health hazards of the NMP-derived extracts were evaluated using a wide spectrum of organisms and assays to determine if fundamental toxicity transcended various species and biological endpoints. The bioassays were also used to characterize partially the chemical nature of biologically reactive compounds in the extracts. The samples tested were unprocessed coal, NMP extracted coal, and NMP-extracted coal following hydrogenation in tetralin at 350, 400, or 450 degrees C; conventional Ravenswood coal tar pitch and Koppers coal tar pitch were also evaluated for comparison with the pitches produced by NMP extraction. These samples were pulverized with a glass mortar and pestle and extracted in dimethyl sulfoxide, and the dimethyl sulfoxide extracts were evaluated by bioassay. Elemental analysis was performed on samples, and selected samples were analyzed by gel permeation chromatography and Fourier-transform infrared spectroscopy. Unprocessed and NMP-extracted coal exhibited little, if any, biological reactivity in any of the bioassays. Material hydrogenated at 350 degrees C was weakly reactive, 400 degrees C material was moderately reactive in all assays, and 450 degrees C material was highly reactive in all bioassays, indicating a correlation between biological reactivity and temperature of hydrogenation. In most assays the NMP extracts derived from 450 degrees C hydrogenated coal exhibited biological reactivity comparable to that of Ravenswood coal tar pitch. Hydrogenation was associated with reduction of number average molecular weight and increased aromaticity of materials. Toxicity of samples correlated well with their ability to induce ethoxyresorufin O-deethylase activity, suggesting polyaromatic hydrocarbons contributed significantly to the biologically reactive chemicals in the extracts. Furthermore, Salmonella reversion assays using tester strains with normal, elevated, or deficient levels of O-acetyltransferase or nitroredudase indicated the mutagenic compounds in NMP extracts of coal hydrogenated at 450 degrees C were primarily attributed to aromatic amines and that lower amounts of these mutagens were present in samples hydrogenated at or below 400 degrees C. These findings suggest that NMP-based processing of coal hydrogenated at high temperatures is Likely to produce hazardous materials, whereas processing based on hydrogenation at lower temperatures greatly reduces the production of hazardous materials. These findings must be considered in the design of safe pilot or commercial plants.