A ten-person odor panel, trained in the characterization of dilute diesel exhaust samples according to the PHS quality/intensity rating kit and the PHS light-extinction smokemeter, were used to measure odor and smoke. Evaluation was made of several two-cycle powered municipal buses equipped with automotive type catalytic devices. The smoke suppressing ability of a barium diesel fuel additive was successfully demonstrated in a five-truck fleet. Power rating had a pronounced effect on visible smoke output, although it appeared to have little or no effect on perceived odor. A limited study of the effect of injecting air in the exhaust at the underside of exhaust valves of a two-cycle powered municipal bus had a negligible effect, while a brief evaluation of the Jacobs engine brake also resulted in no noticeable change. Special studies were conducted and reported, including the effect of exhaust pipe size on smoke readings, preliminary studies of a tentative PHS smoke procedure, attempted evaluation of an electrostatic precipitator, and base line odor, smoke, and emissions from a municipal coach powered by a four-cycle V8 engine. (Author)