Environmental tobacco smoke (ETS) from an electrically heated cigarette (the Accord smoking system: U.S. test market, 2 mg tar) and a conventional lit-end cigarette (Merit cigarette: German market, 7 mg tar) was investigated. The Accord cigarette is made of conventional tobacco filler rolled in tobacco mat and smoked in a battery-operated lighter, which heats the tobacco during puffing. Because the tobacco does not burn continuously, the Accord smoking system delivers essentially no sidestream smoke. ETS was generated by 3 smokers each smoking 2 cigarettes in a 22 m(3) unventilated room. Constituents that could be measured with sufficient sensitivity were chosen from a list of commonly used markers for ETS or from a list of approximately 50 potentially toxicologically relevant mainstream smoke constituents. Concentrations of constituents were lower for Accord cigarettes than for Merit cigarettes: background-corrected concentrations of total particulate matter by 93 to 96% (determined by the Toem method, UV absorption, or fluorescence), solanesol by 89%, acetaldehyde and isoprene by 96%, and nicotine by 98%. For the majority of constituents, there was no difference between ETS generated by the Accord smoking system and background. Concentrations of carbon monoxide and benzene were lower by > 94%, toluene by > 96%, 3-ethenyl pyridine by > 98%, and 6 polyaromatic hydrocarbons (including benzo(a)pyrene) by > 97 to > 99.5%. The electrically heated cigarette produced substantially less ETS than the conventional cigarette as shown for 15 constituents.