The changes in peroxidase and catalase activities, and isoperoxidase patterns in different parts of mung bean seedling caused by the treatment with plant growth substances, GA₃, and ABA, were examined. As germination proceeded, the activity of peroxidase in all part except hypocotyl was increased, while that of catalase decreased. The separate application of GA₃, and ABA increased the activity of peroxidase which was more influenced by GA₃, than by ABA only in cotyledon, while that of catalase was more affected by ABA than by GA₃. Electrophoretic study revealed that the number of isoperoxidase was increased continuously in all parts during development. A greater influence was exerted on the intensity of isozyme than the number of isozyme by the hormonal treatment.