The capacity of laboratory tests and clinical signs to predict allergic manifestations up to 18 months of age was assessed in 129 newborn babies, most of whom had family members with atopic disease. The parameters assessed included family history; skin dryness; erythema toxicum; skin reactivity to histamine and IgE levels; eosinophil counts; and peripheral white blood cell, leukocyte differential, and platelet counts in cord blood (CB). Erythema toxicum and white blood cell and platelet counts were of no value as predictors of allergy. The sensitivity of family history, skin dryness, and sensitivity to histamine, as well as IgE levels and eosinophil counts, varied 25-79% and the specificity 40-74%. The efficiency was never higher than 58%. Logistic regression, applied in order to evaluate the joint predictive power of the five parameters, showed a P value of < 0.001. The estimated probability for atopy before 18 months of age was 0.33 for neonates with normal skin texture, a CB IgE of less than 0.5 kU/l, and a history of fewer than two family members with atopy. The probability increased to 0.89 for babies with a dry skin, a history of two or more atopic family members, and a CB IgE of > or = 0.5 kU/l. In conclusion, not one parameter nor any combination of them seems suitable for general screening. However, a combination of family history and CB IgE and skin assessment may be used to identify babies at high risk of allergy for participation in prevention studies.