PIP: This article discusses the impact of cooking stoves in developing countries on indoor air quality and human health. About 50% of the world's households rely on wood, stubble, dung, and grass for cooking fuel. These products are burned in open fires and inefficient stoves in poorly ventilated rooms. Biomass smoke contains many harmful pollutants, such as particles and carbon monoxide. Coal smoke contains sulphur and nitrogen oxides and hydrocarbons that can cause cancer. Biomass smoke can cause acute respiratory infections. Women and children receive the highest exposure to biomass smoke. About 2500 million people are exposed to excessive levels of indoor air pollution, of which most is due to burning biomass and coal indoors with poor ventilation. About 1.9 million deaths annually are attributed to rural indoor air pollution from suspended particulate matter. About 450,000 deaths annually are attributed to urban indoor air pollution. An additional 500,000 deaths are attributed to other suspended particulate matter and sulphur dioxide in the atmosphere. Particulate suspensions in the air are especially problematic in rural African countries and rural India. Particulates are acutely problematic in urban Latin America, India, and China. One study in The Gambia found that girls younger than 5 who were around mothers who were cooking had a 6-times higher risk of acute respiratory infections (ARI) than those around parents who smoked cigarettes. It is the products of incomplete combustion that pose the greatest risk to health. A 1993 study in Kenya found that the use of the jiko stove lowered ARI and conjunctivitis. The Indoor Air 99 Conference in Edinburgh is planned for August 1999 and will emphasize the health hazards of indoor air pollution. Behavioral change is not easy. The first step is persuading people that biomass smoke exposure is harmful and a serious health hazard.