This material reports findings of an explanatory experimental study designed to add information on the contribution to air pollution of exhaust emissions from small, utility engines, and to evaluate the procedures used to test small engines. Gross measurements of hydrocarbon, carbon monoxide, and nitric oxide are reported for 29 4- cycle and 7 2-cycle engines; sizes of the engines ranged 2 to 22 hp. Emission measurements were made on each engine for nine combinations of load and air-fuel adjustments; only one speed point-- full governed--was covered in the tests. Test procedures are described. An overall average of the data indicate that, operated at full-load and optimum air-fuel ratio, the 4-cycle engines emitted amount 8 grams hc, 180 grams CO, and 5 grams NO2 per horsepower- hour. Under comparable conditions, the 3 to 6 hp 2-cycle engines emitted an average of 140 grams hc, 240 grams CO, and 2 grams NO2 per horsepower-hour.