Apical dominance phenomena have been studied in seedlings of Vicia faba particularly in relation to the movement about the plant of uracil-2-14C applied to the cotyledons. Decapitation just below the second node releases the growth of the lowermost lateral bud and inhibition is completely reimposed by application of indole-3-acetic acid (IAA) to the cut surface. Uracil-2-14C applied in solution to the cotyledons is distributed in the stems of all experimental seedlings with no consistent differences due to decapitation or IAA application. On the other hand, decapitation results in a rapid increase in uracil-2-14C content in the lateral buds which far exceeds their promoted growth. This uptake is completely suppressed by IAA application. A ring of tri-iodobenzoic acid (TIBA)-lanolin paste around the stem above the bud suppresses IAA action both in bud growth and on uracil-2-14C uptake, and also on the movement of IAA-1-14C down the stem. TIBA-application to the base of the bud does not prevent IAA action on bud growth, but also does not prevent the movement of IAA-1-14C (or a water soluble product of its metabolism) into the bud. Direct application of kinetin to the lateral bud of intact plants causes a short-lived release of growth. Gibberellic acid produces a smaller and scarcely significant increase which is additive to the kinetin effect. Neither has any effect on uracil-2-14C movement into the bud. The implications of these findings are discussed in relation to various existing theories of the mode of auxin action in apical dominance and it is concluded that their strongest support is for a mechanism involving the suppression of phloem differentiation in the vascular supply to the bud.