Abstract Over a 1-yr period, measurements of indoor air pollutants (CO x , NO x , formaldehyde, volatile, organics. particulate matter, and radon) were made in 40 homes in east Tennessee. The houses were of various ages with different types of insulation and heating. Sixty percent of the houses exceeded 100 nL/L of formaldehyde on at least one occasion. Over the duration of the study, houses older than 5 yr averaged 40 nL/L of formaldehyde while houses less than 5 yr old averaged 80 nL/L. The highest concentration of formaldehyde was 400 nL/L, measured in a new home. The highest levels of formaldehyde were usually recorded during summer months. The concentration of various organics in indoor air was at least tenfold higher than in outdoor air. Carbon monoxide and nitrogen oxides were usually <2 μL/L and <20 nL/L, respectively, except when gas stoves or kerosene space heaters were operating, or when a car was running in the garage. In 30% of the houses, the radon concentration exceeded 4 pCi/L. The mean radon level in houses built near ridgelines was 4.4 pCi/L, while houses located in the valleys had a mean level of 1.7 pCi/L. The factor having the most impact on infiltration was operation of the central duct fan of the heating, ventilation, and air conditioning system. For measurements made before December 1984, the mean rate of air exchange increased from 0.39 to 0.74 h −1 when the duct fan was operated.