Whereas illumination of mature leaf discs and prolonged illumination of spinach beet seedlings gave rise to co-ordinated increases in PAL and C4H followed later by increases together in pC3H and o-diphenol oxidase, relatively brief illumination of seedlings with white or red light gave co-ordinated increases in PAL, C4H and pC3H without any increase in DOPA oxidase. The pC3H induced in young seedlings has been partially purified and shown to be a copper protein with relatively low DOPA oxidase activity, but chromatographically separable from other phenolases present. The enzyme was similar to these other phenolases but distinguished by its inability to catalyse the 3-hydroxylation of tyrosine. This phenolase with low oxidase activity was induced mainly in the hypocotyl and is possibly concerned with lignin biogenesis, whereas the high-oxidase phenolases present in the cotyledons or induced in leaves may play some role in the protection of the tissue following physical damage.