Effects of folic acid on the phenylalanine tolerance test in phenylketonuria.

Phenylalanine tolerance tests were performed on four untreated children with phenylketonuria, aged 8 to 12 years, before and after 14 days of folic acid administration (70 mg./day). No significant changes were noted in the phenylalanine tolerance tests or in the general condition of the patients. This study was carried out because of recent findings that a folic acid derivative is a co-factor in the conversion of phenylalanine to tyrosine.