In order to study the effect of the indoor pollution, particularly by parental smoking, on respiratory diseases of children, the relationship was examined between smoking by family members, use of various types of stoves and air conditioners, and the prevalence rate of respiratory diseases in 7,916 three year old children who, for health check up, visited the Chita Public Health Center located in the Aichi Prefecture in 1978-1979. Results of this study suggested that among various sources of the indoor pollution, smoking by mother had the strongest effect on respiratory diseases, especially asthmatic bronchitis of young children, while the use of various types of stoves including non-ventilated kerosene stoves was not related significantly to the prevalence rate of respiratory diseases of those children except an increased rate of frequent common cold in children of households having an air conditioner(s).