The report discusses problems associated with testing fuels, fuel additives and their combustion products for potential public health problems. Conclusions follow: (1) Initial evaluation of safety of a new fuel-additive combination should include comparison between a standard fuel and the new combination. (2) Biologic methods suggested for initial evaluation should be sensitive to the possibility that known human health effects from such sources may increase or diminish. (3) Separate considerations and more extensive research on most metal-containing additives should be required because of their persistence in the environment and their tendency to accumulate in the body. (4) All methods will need careful validation and inter-laboratory studies. (5) Interpreting results of studies on combustion products is difficult at best; decisions should be made by informed scientists. (6) Appropriate epidemiologic and analytic studies should be conducted whenever new fuel-additive combinations are introduced.