Report to the Medical Research Council of the Conference on Phenylketonuria: Treatment of Phenylketonuria, p. 1691. The proceedings of a conference on phenylketonuria under the auspices of the Medical Research Council of Great Britain is summarized. Three aspects of the metabolic disorder are stressed: detection, control of treatment, and diet. The optimum date for testing of infants lies within the first 6 weeks of life. The appearance of phenylpyruvic acid in the urine occurs between the second and sixth weeks. If practicable, screening of urine should be performed between the tenth and fourteenth days of life and again at 6 weeks of age. Special emphasis should be placed upon babies born into families with a history of phenylketonuria. Reagents such as ferric chloride, dinitrophenylhydrazine, and phenistix (a modification of the ferric chloride test) are recommended. Advice on factors responsible for faise-negative and false-positive reactions is included. In Great Britain testing is carried out through the local health authorities. Treatment of phenylketonuria should not be instituted until plasma estimates of phenylalanine are performed and the diagnosis thereby confirmed. Recommended procedures for the plasma determination are described. A subcommittee has also reported on low phenylalanine diets with relation to physical growth and development during infancy and the results of therapy. Edward E. Wallach