In unpollinated Nicotiana alata styles peroxidase activity was relatively high in the epidermis, the vascular system and the transmitting tissue. Especially the cell walls of these tissues contained considerable amounts of peroxidase. In the transmitting tissue the peroxidase activity was also high in the cytoplasm and in the intercellular substance. Extraction of the cell walls by means of a vacuum infiltration method revealed the presence of four peroxidase isoenzymes in the walls of cortex including vascular traces. After pollination the activity of several cortical peroxidase isoenzymes increased in both cytoplasmic and wall fractions. Generally, the amounts of the peroxidase isoenzymes extracted from walls of cross-pollinated styles exceeded those extracted from self-pollinated styles. In pollinated styles the peroxidase positive intercellular substance of the transmitting tissue was replaced by the pollen tubes. The possible role of peroxidase in the intercellular substance is discussed in relation to the physiological function of the transmitting tissue.