Hazardous contaminants generated in synthetic fuel plants during coal gasification were identified, and toxicological and epidemiological information on the more important substances were reviewed. The major characteristics of three coal gasification processes that use current technology are described. The unit operations approach was used to evaluate coal gasification. The approach involves the definition of the chemical process and reactions of basic chemical compounds; definition of input and output streams and of each unit, and speculation on chemical compounds formed; and definition of all possible sources of leaks, vents, or discharges of gases, solids, or liquids to the atmosphere for each unit. The potential hazards inherent in each stage of the coal gasification process are projected. The author concludes that the range of toxicants and possible health effects is extremely wide, from carbon monoxide to complex mixtures of organic carcinogens, and there are undetermined mutagenic and teratogenic properties associated with these substances. Control technology, prospective mortality studies, medical surveillance, and employee health education programs are recommended as precautionary measures in view of the variety of unknown variables involved in coal gasification.