Bronchial asthma, one of the most common illnesses in the western world, affecting between 8-10% of children and 3-5% of the adult population, is increasingly becoming a public health problem in the developing world. Its incidence continues to rise throughout the world and, indeed, it has been estimated that it has increased by approximately 50% over the last 10 years. The reasons underlying this alarming trend are probably related to the many possible interactions between allergens and pollution be they domestic (eg passive smoking) or atmospheric (most notably motor vehicle exhaust emissions). The severity of asthma is also increasing as is witnessed by the higher levels of hospitalization of sufferers and the increased death rate (approximately 2000 fatalities per year in France alone). Asthma changes the quality of life of patients whatever their age and is an important cause of school absenteeism and lost working days. The costs due to asthma, which currently represent approximately 1% of direct and indirect health care costs (7 thousand millions French francs), are also steadily mounting. These pessimistic facts and statistics have inspired the drafting of an "International Consensus" on the treatment of asthma sufferers and have caused the WHO to take a position drawing maximum public attention to this disease and measures for its control and prevention.