This report is based on a pilot project for a large epidemiologic study of inner-city asthma, in which exposures to air pollutants will be related to both incidence and prevalance of asthma. Nitrogen dioxide concenmuions were measured in three rooms as well as outdoors in 44 inner-city apartments with gas cooking stoves. Fifty-two separate month-long series of 48-h time-integrated NO, sample. (Palmes tubes) were gathered from fall 1982 to spring 1984. The 48-h average N02 concentrations taken within homes frequently exceeded the U.S. EPA outdoor annual mean NO, standard of 100 μ.g/m3, and were observed to reach levels as high as 300 μ.g/m3 in some homes. Short-term peaks of N02 were as high as 2000 μ.g/ m3 at 2. 3 m from the floor and 1700 μ.g/m3 at 1. 7 m from the floor in kitchens. Activity records filled out by study subjects indicated an unusually large percentage of time spent indoors at home by inner-city residents, many of whom were asthma patients. On the basis of these activity patterns and the regular occurrence of high NO, levels in inner-city apartments, individuals in this population are likely to have elevated personal exposure to this combustion by-product.