[The phenylalanine stress test in the classification of patients with phenylketonuria].

Classification of defects of phenylalanine hydroxylase is usually performed by a phenylalanine loading test according to Blaskovics. This loading test has some drawbacks, especially negative side effects for the patients. We found a correlation between the result of the loading test and the dietetic phenylalanine tolerance. Therefore the trouble of undergoing the loading rest may be spared many patients.