Among various microbial cells examined under screening conditions, Nocardia opaca showed the highest activity for production of phenylalanine from phenylpyruvate. Here NH4Cl as well as amino acids were used as an amino donor for phenylalanine production. The phenylalanine production rate increased with increasing hydrogen pressure. The specific activity of phenylalanine dehydrogenase was increased by culturing N. opaca cells in nutrient broth containing 0.3% phenylalanine. As a result, the phenylalanine production rate increased from 0.69 to 4.4 μmol/min g dry cells. Immobilized cells were activated in nutrient broth containing ZnCl2 before phenylalanine production. Phenylalanine dehydrogenase activity and cell number in the gel increased with increasing incubation time, and the maximum phenylalanine dehydrogenase activity was obtained at 36 h incubation. Then, phenylalanine was produced from phenylpyruvate, NH4Cl, and 100 atm H2 with the activated immobilized cells. The rate of phenylalanine production was 0.24 μmol/min cm3 gel. The conversion of phenylpyruvate to phenylalanine was 82%. Immobilized cells retained 76% of the initial phenylalanine production rate after 10 h reactions were repeated 11 times with two intervening reactivations.