The growth of Lycopersicon esculentum Mill. seedlings was inhibited by treatment with uniconazole and prohexadione calcium. The effect of uniconazole was more severe than that of prohexadione calcium. Gibberellin-like activity in seedlings was differently suppressed by treatment with uniconazole and prohexadione calcium. The inhibitory effect of these compounds seemed to be caused by the decrease in gibberellin-like activity.