The purpose of this study was to investigate the value of a new multiantigen radioallergosorbent test, Phadiatop Paediatric, in the diagnosis of atopy in children less than 7 years of age. The diagnosis of atopic disease was established by history, physical examination, total serum IgE concentration, and the results of prick skin tests or radioallergosorbent tests or both, and then compared with the result of the Phadiatop Paediatric test for each patient. One hundred two patients (62 boys) between the ages of 4 months and 7.3 years were enrolled (median age 3.2 years). After the history and physical examination, 42% of the patients were believed to be atopic and 32% to be nonatopic; the diagnosis was uncertain in 26%. Skin prick test reactions to a variety of foods and inhalants were positive in 41 of 63 children tested; results of radioallergosorbent tests were positive in 35 of 61 children. Overall, atopy was diagnosed in 53 children and 49 were found to be nonatopic. When the clinical diagnosis was used as the gold standard, the Phadiatop test resulted in a correct diagnosis of atopy in 49 of 53 cases and of no atopy in 43 of 49 cases: sensitivity = 92%, specificity = 88%, and efficiency = 90%. Although the Phadiatop Paediatric test does not indicate specific sensitivities, it provides the clinician with a useful screening test for atopic disease in children 7 years of age or less, and the researcher with a means of validating atopic populations.