To predict and prevent the onset of allergic diseases, we studied the effects of indoor environmental factors, such as diet, on pregnant women and carried out follow-up studies on their infants. Blood samples were collected at random from women who were diagnosed as pregnant (n = 2045). Umbilical cord blood was collected at delivery (n = 1453). To evaluate the efficacy of food guidance, the pregnant women were divided into two groups--one receiving simple diet guidance starting in the later stages of pregnancy, and one receiving no guidance whatsoever. A follow-up survey on allergic symptoms was done on their two-year-old infants, revealing a lower incidence of symptomatic manifestations in the diet guidance group (p < 0.001). Respiratory symptoms (p < 0.05) were associated with maternal smoking and outside work during pregnancy. A study on food guidance in combination with environmental factors revealed that the incidence of respiratory symptoms in two-year-old infants whose mothers received diet guidance in a good indoor environment was held down to around 36.1%, while the incidence in infants whose mothers received diet guidance in a poor indoor environment was 48.1%.