The effect of reagent penetration into the resin on the reaction kinetics was studied by examining four solid-phase organic reactions on resin beads of various sizes. In three esterification reactions, the declining trend is observed only for the smallest acid used. As the acids become bulkier, no dependence of the reaction rate on the bead size was observed, indicating that when the reaction rate becomes limiting, the diffusion does not control the kinetics. In a bromination reaction, a reagent salt is composed of a triphenylphosphous cation and a bromide anion. We observed that organic salts are capable of penetrating resin and facilitating the reaction, but there is no clear correlation with bead size.