In a study of cows' milk allergy (CMA) in infancy, 135 consecutive challenges were performed on children with a good clinical history of the disorder. Of these, only half of the patients were shown to have the disease. Highly atopic patients responded rapidly to small volumes of milk with acute urticaria, wheezing, stridor and eczema, whereas patients who were relatively non-atopic developed symptoms of eczema, bronchitis and wheezing over several hours or days. In a statistical evaluation of the diagnostic value of skin tests and RAST it was shown for the extracts used in this investigation, and for the population studied, all patients with SPT greater than or equal to 4 had CMA. The results highlight the potential diagnostic value of SPT in the identification of children with some forms of CMA if standardized cows' milk allergen extracts can be prepared.