To determine the effects of knock in a spark-ignition, single-cylinder engine with cooled exhaust upon the exhaust composition, exhaust products (CO, CO2, and total hydrocarbons) were measured by non-dispersive infrared analyzers (NDIRA) and by a flame ionization detector (FID). Individual hydrocarbons were separated on a gas-liquid chromatograph.In fuel-rich mixtures, the FID indicated noticible decreases in the hydrocarbon concentrations in the presence of knock. The NDIRA did not indicate a decrease in the hydrocarbons at knock of lower intensities but showed decreases in hydrocarbons at knock of higher intensities. Chromatograms indicated a preferential decreases in acetylene at the time of knock, causing different responses at lower intensities. In fuel-lean mixtures, no apparent effect of knock on the hydrocarbons was indicated.Thus, it was concluded that in fuel-rich to stoichiometric regions, knock generally decreases the hydrocarbon concentration in the exhaust and the extent of the decreases is greater with the intensity of knock.