Comparison was made of IgE and IgA levels in aspirated and gravity-collected cord blood (CB) from the umbilical vein and in capillary blood samples collected on the 4-5th day of life among 21 infants with atopic heredity. The IgA levels, but not the IgE levels, were significantly (p < 0.001) lower at days 4-5 of life than at delivery. Further, there were significantly (p < 0.05) more infants with decreasing IgA levels (20/21; 95%) than IgE levels (9/15; 60% of those with detectable IgE, i.e., > or = 0.125 kU/l). These observations, together with the highly significant correlation observed between IgE in aspirated CB samples and at 4-5 days of age, suggest active IgE synthesis during the prenatal and postnatal periods. Contamination of CB with maternal blood, defined as an increased CBIgA level (> or = 14.1 micrograms/ml), was found in 3 (14%) CB samples, all of which were gravity-collected. Of 4 CB samples (gravity-collected) with elevated IgE (i.e., > or = 0.9 kU/l), 2 had suspected maternal contamination. Therefore, aspiration of CB or capillary collection at 4-5 days of age should be preferred for allergy prediction. If gravity collection is used, contamination should be investigated by determining IgA in all CB samples with IgE concentrations exceeding the cut-off point.