Summary One nonenzymic and two enzymic forms of ascorbate peroxidase were found in pea leaves, and designated A, B and C. Form A was due to a low molecular weight, heat-stable component, and could be separated from the enzymic forms by gel filtration. Forms B and C were soluble proteins with an apparent molecular weight of 57,000. These two forms could be separated by cation-exchange chromatography on CM-Sephadex C-50. This technique was incorporated into a procedure for their partial purification. Several properties of B and C were found to be similar: they were active over a wide pH range (5 to 8), they displayed very high affinities for H 2O 2 (Km<5 μM), and Km values for ascorbate (6.5 mM and 2.9 mM, respectively) were comparable to physiological concentrations of this substrate. These properties are considered conducive to the proposed physiological role of ascorbate peroxidase, viz prevention of H 2O 2 accumulation.