The effects of 3‐hydroxy‐β‐ionone on the growth of hypocotyls of dark‐grown dwarl bean (Phaseolus vulgaris L. cv. Morocco) and tall bean (cv. Kentucky Wonder) were examined. 3‐Hydroxy‐β‐ionone inhibited growth of the hypocotyl of both cultivars at doses higher than 3 ng per plant. Seedlings of the tall cultivar responded to a slightly lesser extent to 3‐hydroxy‐β‐ionone than those of the dwarf cultivar. Changes in the levels of 3‐hydroxy‐β‐ionone in hypocotyls of both cultivars 24 h after the onset of light irradiation, were determined by high‐performance liquid chromatography and the results compared with the results of light‐induced inhibition of growth. The difference in levels of 3‐hydroxy‐β‐ionone between the two cultivars was considerable, and the changes in its levels in the hypocotyls of each cultivar reflected the light‐induced inhibition of growth of the hypocotyls of the respective cultivars. These results suggest that the endogenous growth inhibitor. 3‐hydroxy‐β‐ionone, may play an important role in the inhibition by light of hypocotyl growth of the two cultivars and may serve to distinguish the growth habits of these cultivars.