We tested the morphogenetic and cell elongating activity of 1,2-benzisoxazole-3-one, a compound similar to 1,2-benzisoxazole-3-acetic acid but lacking the lateral carbon chain. For comparison, we tested also the activity of indole 2,3-dione, having the same indolic ring as indole 3-acetic acid but no lateral carbon chain. The tests were made on the regeneration of tomato (Lycopersicon esculentum Miller var. Alice) from cotyledons and on pea (Pisum sativum L. var. Alaska) stem elongation. We found that 1,2 benzisoxazole-3-one retains part of the high shoot inducing activity of 1,2-benzisoxazole-3-aceticacid, while indole-2,3-dione is inactive. Both compounds have no effect on root induction or cell elongation. It seems therefore that the activity of 1,2 benzisoxazole-3-acetic acid is partly related to the structure of its ring, and that also in this respect 1,2 benzisoxazole-3-acetic acid differs from other auxinlike compounds.