Week-long integrated nitrogen dioxide (NO/sub 2/) measurements were made by using diffusion tube samplers inside and outside 137 homes in Portage, WI, over a 1-year period. The annual mean ambient NO/sub 2/ concentrations in this rural community were 10-15 ..mu..g/m/sup 3/. NO/sub 2/ levels inside the kitchens of 112 homes with gas stoves averaged about 50 ..mu..g/m/sup 3/ higher, and bedroom levels were about 30 ..mu..g/m/sup 3/ higher, than outdoor levels. Ten percent of the gas-cooking homes had annual average kitchen NO/sub 2/ levels higher than the National Ambient Air Quality Standard of 100 ..mu..g/m/sup 3/. NO/sub 2/ levels inside kitchens of 25 homes with electric stoves were about two-thirds outdoor levels, while corresponding bedroom levels were one-half outdoor levels. Distinct seasonal patterns (higher indoor levels in winter, lower in summer) consistent with changes in normal air-exchange rates were evident in gas-cooking homes. The large variation of NO/sub 2/ concentrations among homes, likely due to differences in stove use, emission rates, and air-exchange rates, limits the development of prediction models. In addition, this variation would reduce the power of epidemiological studies of respiratory health, which use ambient NO/sub 2/ concentration levels, a simple dichotomous description of stove type and twomore » categories of home cooking fuel to describe exposure.« less