Carbon monoxide and nitrogen dioxide were monitored in 12 homes on a real-time basis to determine their transient concentrations, their dispersion through the homes and day-to-day variation in pollutant levels. Kitchen ventilation was determined using sulphur hexafluoride tracer gas, and use of unvented gas appliances was monitored with thermo couples. A week-long measurement programme was undertaken in a wide range of homes to determine the distribution of carbon monoxide, nitrogen dioxide, particulates and organic compounds. Tracer gas experiments were undertaken in kitchens and additional information about the homes and occupant activities was gathered with inspection lists, questionnaires and diaries. The objective was to determine the variability of pollutant levels within and between seasons.