Prunin (naringenin 7-glucoside), which was identified in dormant peach buds, was found to act as a growth inhibitor of wheat coleoptile elongation.Quantitative estimation on a fresh weight basis of the flavonoid in peach buds revealed a high level in late summer, a steep decrease in autumn that became more moderate during the winter, with lowest values near bud swell in spring. Two periods of reaccumulation of prunin during October and January fitted 2 periods of arrested growth of the resting bud. A negative correlation was demonstrated between prunin and naringenin levels during August through October. It is proposed that prunin might act as a precursor for naringenin that accumulates in resting buds in autumn. It is suggested that the system glucoside-aglucone-beta glucosidase might have regulatory properties in the dormant bud.