This paper concerns a class of metabolic inhibitors which possess the ability to suppress the flowering of short-day plants and which appear to do so by interfering with generation of the flowering stimulus by the leaf. The inhibition of flowering with which we are here concerned is thus different from that elicited by 5-fluorouracil and 5-fluorodeoxyuridine. These two substances act by preventing successful receipt by the bud of the leaf-produced floral stimulus (4, 17). The substances here reported as active in inhibition of the generation of flowering stimulus by the leaf are of further interest in that they are inhibitors of the biogenesis of steroids.