Cord total serum IgE has been advocated as a screening test to detect infants at high risk of allergy who would be suitable for preventive measures. In a population based prospective study to look at the predictive capacity of cord IgF and family history of atopy 1111 one-year-old infants were followed-up. Cord IgE was measured using the EIA ultra technique (Pharmacia, Uppsala, Sweden). Atopic symptoms developed in 255 (23%) at one year, 183 (16·5%) had probable atopy (clinical disorder but negative skin prick test (SPT)) and 72 (6·5%) had definite atopy (clinical disorder with positive SPT), There was no difference in the mean cord IgE levels in infants with or without atopic manifestations. The cut-off for IgF was taken at 0·6 ku/1. The specificity of the test was 92% but the sensitivity was only 8·5%. The positive and negative predictive values were 24% and 78% respectively. Family history of atopy is far more sensitive in detecting infants at risk of atopy and little is added by knowledge of cord IgE.