The use of several gibberellin-biosynthesis inhibitors in the sensitized rice (Oryza sativa L.) seedling bioassays was investigated. Paclobutrazol at 3.4 mM and ancymidol at 0.7 mM made rice seedlings almost as sensitive to gibbrellins as 80 muM uniconazole did. Use of these two chemicals will be practicable in gibberellin bioassays as well as uniconazole.