Physiological dormancy of freshly-harvested seeds of Stylosanthes humilis was partially broken by 1-aminocyclopropane-1-carboxylic acid (ACC). This ACC effect was inhibited by abseisic ac id (ABA) in a reversible way, The inhibiting effect of ABA on germination of dormant seeds pretreated with ACC was significantly larger than the stimulating effect of ACC on seeds pretreated with ABA.