Elemental mercury is an important Persistent, Bioaccumulative and Toxic indoor pollutant. Measurements of ambient and indoor mercury vapor concentrations were made in 23 homes in Brooklyn, New York. For dwellings, measurements were performed at the breathing zone of infants, toddlers and adults (6", 2', and 5', respectively). Measured mercury vapor levels ranged from 4 - 112 ng/m3 (mean: 25 ng/m3) for indoor air and N.D. (none detect) - 11 ng/m3 (mean: 5 ng/m3) for ambient air. On average, the indoor level was five times the amount found in ambient air. Little variation in mercury concentration with respect to height from the floor was observed.