It has been noted that eye and respiratory irritation frequently occurred in the ground crews and pilots working on the field behind an aircraft with a low smoke combustor (LSC) engine. This study was attempted to analyze the exhaust sampled at about 50 m behind the LSC J79 engines at idle power setting by means of a high performance liquid chromatography (HPLC) technique. Nine kinds of lower aliphatic carbonyl compound (seven aldehydes and two ketones) were identified. The concentration of formaldehyde was the highest among them, showing the value above the threshold reported by previous investigators. Concentration of NOx was simultaneously measured by a gas detector tube in the same sample. The exhaust of a conventional J79 engine, which has rarely caused irritation, was also analyzed by the same technique and the results were compared. It was concluded that formaldehyde plays a major role in causing irritation.