The potential for domestic biogas is enormous in Cambodia with 1 million households that have sufficient livestock to feed for the smallest biogas digester. Biogas could therefore help to address HAP in Cambodia to millions of rural inhabitants. The National Biodigester Programme (NBP) of Cambodia, a partnership between SNV and the Ministry of Agriculture Forestry and Fisheries, is implementing a market-based programme and has so far reached over 100,000 Cambodians with 23,000 biodigesters installed. This study was set-up to quantify the health impact of NBP by measuring the reduction of hazardous pollutants, CO and PM2.5 of households that use biogas and matching households in terms of family size, socioeconomic conditions and cooking conditions without a biodigester. The study took place in 5 randomly selected villages in which 5 households of both groups the kitchen concentration, exposure to the pollutants by the main cook and the ambient air was measured for 48 hours. The study showed that biogas reduces PM2.5 levels, with a reduction of around 36% reduction in exposure and 88% reduction in kitchen concentrations. CO levels are also much lower, but in most cases, including the baseline households lower than the 24-hour WHO guidelines. Short-term exposure to CO (≤ 1 hour) however remained too high for almost a quarter of the baseline households.