Eleven study subjects with asthma and 12 normal controls were monitored for 5 days with a portable continuous nitrogen dioxide (NO2) monitoring instrument held at breathing level before, during, and after cooking dinner on a gas cooking range. Forced expiratory volume in 1 sec (FEV1.0), forced expiratory volume (FEV25-75), peak expiratory flow, and a tracing of the entire flow curve was monitored before the gas stove was turned on, during a break in cooking, immediately after, and 1 hr after cooking was completed. Study design for detection of health effects of the acute exposures to NO2 described above and a method of validating findings in an exposure chamber are discussed in this paper.