Each year, over six million children in the world die of acute respiratory infections (ARIs). It is the most commonly diagnosed condition in children. In 1984-5 in the State of Guerrero ARIs were responsible for 28% of all infant deaths. Every young child suffers ARIs; the thrust of CIET research has been to reduce the severity of the episodes. In 1986 a CIET research team carried out a survey in 41 sentinel communities to study the prevalence of ARIs in children under five years old; to determine the risk factors for the illness and to measure the extent of protection offered by the measles vaccination. Of 4,036 children studied, 43% had suffered ARIs in the two weeks prior to the survey. The results indicated that children most at risk were those who slept in the same room as others, were undernourished and had not been vaccinated against measles. The measles vaccination offered a significant protection against ARIs as well as decreasing the severity and duration of the illness in those children who contracted the illness. Tepid sponging of a sick child also reduced the duration of the illness.