Peroxidase activity was localized in the shoot apical meristem (SAM) of Spinacia at the light and electron microscope level with the histochemical method employing H₂0₂ and 3,3'-diaminobenzidine. At the light microscopic level, peroxidase activity was examined in unfixed cryostat sections at different pHs. The enzyme was found to be more intense at low than at neutral and high pH. The activity was evenly distributed over the different regions of the meristem at low pH, whereas it was more intense in the rib meristem at pH 6.8 and 7.2. At the ultrastructural level, peroxidase activity was found at 3 cellular sites: the cell wall, the tonoplast and the plasmalemma. These results were discussed in relationship with the in situ distribution of peroxidases in plant cells and other enzymes in vegetative SAM.