Argonne National Laboratory has been evaluating the health and environmental effects of emerging coal-gasification technologies. Representative condensates from the Morgantown Energy Technology Center's fixed-bed gasifier were characterized using advanced techniques, including fractionation, toxicological testing, and computer-assisted instrumental analysis. The samples were a heavy tar from a bituminous coal run (BHT), a composite side-stream tar (CST), an oxygen-blown side-stream condensate (OBS), and an air-blown composite (ABC). Neutral components accounted for most of the mass and much of the mutagenicity. Neutral fractions of the ABC, CST, and OBS samples were very similar, while that of the BHT sample was enriched in high-ring-number polycyclic aromatic hydrocarbons (PAH). Basic components accounted for a very small part of the mass, but for much of the mutagenicity. Basic nitrogen-heterocyclic PAH greatly predominated over the primary aromatic amines. Acidic components accounted for an important part of the mass, but for negligible mutagenicity, except for the BHT sample. The acid fraction of the OBS sample consisted mainly of one- or two-ring phenolic materials, whereas that of the BHT sample consisted of a broad range of hydroxy-aromatics having three to four rings. Mammalian-cell mutagenic activity was observed in the BHT sample after removal of acidic components.