A marked increase in phenylalanine ammonia-lyase and tyrosine ammonia-lyase activities was observed in sweet potato roots in response to wounding and infection. A marked rise of phenylalanine ammonia-lyase activity occurred during a period of 6 hrs. sliced Ceratocystis Fimbriata and infected tissues. The change in activity of this enzyme with time after wounding showed a close parallel with the pattern of accumulation of polyphenols in the tissues. A similar picture was observed with the tyrosine ammonia-lyase, but the activity of this enzyme was very low compared to that of phenylalanine ammonia-lyase. DEAE-cellulose chromatog-raphy indicated that phenylalanine ammonia-lyase was separated into 2 components with phenylalanine ammonia-lyase activity by repeated DEAE-cellulose chromatography. Some properties of 2 types of phenylalanine ammonia-lyase were investigated, and a possible role of this enzyme in the biosynthesis of phenylpropane compounds in sweet potato roots is discussed.