Only 11% of the total peroxidase activity in a root tip homogenate of Zea mays (L.) was sedimentable. The majority of sedimentable activity was bound to membrane fractions with which acid hydrolases were also associated.Peroxidase activity was released from a cell wall fraction exhaustively washed using homogenization and detergent. The specific activities of the washings were 3-10 fold higher than in the sedimentable and soluble fractions. A quarter of the wall associated activity was only released after treatment of the washed wall preparation with cellulase.Histochemistry shows peroxidase associated with cell walls. The only activity within the cell was observed associated with the inner surface of the provacuole membranes. The provacuoles were observed fusing in maturing cells. No peroxidase was seen in the Golgi.One peroxidase isozyme was apparently specifically associated with the sedimentable membrane fractions and may represent the activity observed in the provacuole membranes. Three fast migrating isozymes were restricted to the soluble fractions while at least three slow migrating isozymes were wall associated. One of the latter was specifically released from the wall by calcium nitrate. The relationship between the isozymes is discussed.A scheme for the origin of vacuoles is proposed.