Screening of total IgE in 2814 cord blood samples was analysed by Phadebas IgE PRIST in 2 1-year birth cohorts (1983-1984 and 1985-1986) in Denmark (n = 1189 + 1625). For follow-up we chose all infants with cord blood IgE greater than or equal to 0.5 kU/l and a randomly chosen group of the same size with cord blood IgE less than 0.5 kU/l. A total of 762 infants were clinically evaluated at 18 months of age. A diagnosis of definite atopy, probable atopy or no atopy, including both IgE and non-IgE mediated disease was established. Applying different cord blood IgE cut-off values (0.3, 0.5, 0.8, 1.1) we did not find an excess of atopic infants among those with elevated cord blood IgE irrespective of the chosen cut-off value. Atopic predisposition or family history of atopic disease was defined as at least one parent or older sibling with atopic disease. Significantly more infants with a family history developed atopy at 18 months. In the 2 series the positive predictive values of cord blood IgE greater than or equal to 0.5 were 43% and 46% and the sensitivities were 17% and 15%. The predictive values of having a family history were 48% and 44% and the sensitivities were 55% and 58%.