SUMMARYA comparison was made of the activities of peroxidase, chlorogenic acid oxidase, glucose‐6‐phosphate dehydrogenase and of peroxidase isoenzymes in the transmitting tissue and the cortex of unpollinatedNicotiana alatastyles.Whereas most peroxidase and chlorogenic acid oxidase activity in a style occurred in the cortex, the activity of glucose‐6‐phosphate dehydrogenase, on the contrary, was highest in the extracts of transmitting tissue.Comparison of peroxidase and glucose‐6‐ phosphate dehydrogenase activities in the style extracts with the sum of the activities present in the cortex and transmitting tissue, when measured separately revealed discrepancies which can be explained by the presence of enzyme inhibitors.Starch gel electrophoresis showed that two peroxidase isoenzymes occur in the transmitting tissue, namely No. 12, a major one which was specific for this tissue and a minor one, No. 7 that was also found in the cortex. The peroxidase isoenzyme No. 10, which has previously been suggested to be involved in the regulation of pollen tube growth occurs only in the cortex, thus indicating that it influences the pollen tube growth indirectly.The possible interactions between chlorogenic acid and the enzymes, peroxidase and chlorogenic acid oxidase in relation to pollen tube growth ar