IN our investigations on the occurrence of gibberellins in the Cucurbitaceae1 we found plant growth inhibitors which had pronounced antagonistic activity towards gibberellin action. Various quantities of the inhibitors were present in the seeds of Cucurbita moschata (Duch. ex Poir), Trichosanthes dioica (Roxb.), Trichosanthes anguina (Linn.), Luffa acutangula (L, Roxb.), Momordica charantia (Linn.), Cucumis sativus (Linn.), Coccinia indica (W.&A.), Benincasa hispida (Thunb., Congn.) and Lagenaria siceraria (Mol., Standl.). Twenty milligrammes of Momordica charantia seeds contained enough inhibitors to kill all TN-1 rice seedlings in the presence of 100 p.p.m. GA3.