The influence of a family history of atopy on atopic morbidity, and relationships between diet in infancy and allergic manifestations at the ages of one and five years were prospectively studied in 91 children. A control group consisted of 72 children with no family history of atopy. At the age of one year, atopic manifestations were found in 19% of 163 children, in 23% of those with a family history of atopy and in 14% of those with no such history. Skin problems were more common in children with a family history of atopy (43%) than in the control children (19%). Of the children with a family history of atopy, 23% had prolonged rhinorrhoea during infancy. The corresponding figure in children with no family history of atopy was 10%. Prolonged rhinorrhoea during infancy correlated with parental smoking only in children with a family history of atopy (47% vs. 18%). At the age of five years, atopic disease was found in 17% of 128 children, 24% of those with a family history of atopy and 9% of those with no such history. Atopic eczema was more common in children with a family history of atopy, irrespective of the diet consumed during infancy. Atopic signs were found in about half of all the children with a family history of atopy. If atopy had been present in the family, the child usually exhibited the same manifestation. Onset of atopic manifestations was not prevented or delayed.