6-Methoxy-benzoxazolin-2(3H)-one (MBOA) inhibited the germination of cress (Lepidium sativum L.) seeds at concentrations greater than 0.03 mM. Inhibition was overcome by sucrose, suggesting that MBOA may inhibit sugar metabolism in cress seeds. Induction of alpha-amylase activity in seeds was also inhibited by MBOA at concentrations greater than 0.03 mM. Inhibition of both germination and induction of alpha-amylase activity increased with increasing concentrations of MBOA, and the extent of germination correlated positively with the activity of alpha-amylase in the seeds. MBOA added to a reaction mixture for alpha-amylase assay did not affect enzyme activity, indicating that MBOA does not inhibit in vitro alpha-amylase activity. Cress seeds germinated approximately 16 hr after incubation, and inhibition of alpha-amylase by MBOA occurred within 6 hr after incubation. These results suggest that MBOA may inhibit the germination of cress seeds by inhibiting the induction of alpha-amylase activity, because alpha-amylase plays a key role in the conversion of reserve carbohydrate into soluble sugars, a prerequisite for seed germination.