Polynuclear aromatic hydrocarbons (PAH) and nitro-substituted polynuclear aromatic hydrocarbons (NO2-PAH) have been identified in organic extracts of ambient air particulate matter. Many of the identified PAH and NO2-PAH are potent carcinogens and/or mutagens. Therefore the determination of PAH and NO2-PAH in ambient air is of considerable importance to the characterization of air quality. A study was conducted to estimate the influence of PAH and NO2-PAH concentration in residences as a result of the following parameters: (1)smoking; (2)wood burning fireplaces; (3)home utilities; (4)ambient air intrusion. Eight study homes and two background homes located in Columbus, OH were sampled in March 1984. Test parameters included the presence or absence of smokers, wood burning fire places, and gas or electric utilities. Samples were taken for 24 hours by using a modified EPA/SURC medium volume sampler. A quartz fiber filter was used to collect particulate matter and a polyurethane foam cartridge was used to trap vapors. This presentation will emphasize the analytical methods and the results of the NO2-PAH determinations from both ambient and indoor air samples. The identification and quantification of NO2-PAH were accomplished using an on-column injection, negative chemical ionization gas chromatography/mass spectrometry (NCI GC/MS) technique, in the multiple ion detection mode (MID). A statistical analysis of these data was conducted to evaluate the test parameter effects on NO2-PAH levels.