A simple stochastic recirculatory formalism is used to compare models of regional drug delivery due to Hunt et al. and Boddy and Aarons. It is shown that these two models are equivalent when regional delivery is ideal. The latter model has the advantage of simplicity. However, the former model appears more useful in relating predictions to experimentally accessible quantities. Neither model is sufficiently general to cover all possible topologies of regions associated with drug response and toxicity. Knowledge of this topology is essential in determining the drug targeting index. The underlying assumptions of the models are discussed, and situations where these assumptions may break down are identified. Finally, it is noted that the analysis of regional delivery may also apply to metabolite and prodrug kinetics.