Phadiatop (Pharmacia) is a new in vitro screening test for respiratory allergy which detects in serum the presence of specific IgE to a mixture of common inhalant allergens; results are either positive or negative. Among 100 patients suffering from rhinitis and/or asthma, investigated with 15 skin prick tests (SPT) and RAST for frequent allergens, the Phadiatop was positive in 63: all 63 had at least one positive SPT and RAST (specificity: 100%). Conversely, ther were 67 patients who had a positive RAST for at least one allergen: among these 67 the total IgE concentration in serum was high (greater than 100 kU/l) in 43 (64%) and the Phadiatop was positive in 63 (94%). Phadiatop was negative in serum obtained from 10 cord bloods and 10 non-allergic subjects (disease-free, 15 negative SPT and RAST). Results of the radio-immunoassay originally proposed by the manufacturer were similar to those obtained with a modified enzymo assay using a fluorometric substrate. In the prediction of respiratory allergy, Phadiatop was found to be specific and more accurate than the determination of total IgE in serum.