This article provides an overview of a semiempirical pretargeting model now under development. After a brief review of the pretargeting concept, the strategies available, and the complexities of optimizing the dosage and timing, a semiempirical model is described that is not only capable of optimizing dosage and timing but also capable of predicting the results of pretargeting as a function of most pretargeting variables. The model requires knowledge of the pharmacokinetics of both the pretargeting agent (usually an antibody) and the effector, the accessibility of the pretargeting antibody for the effector, and their quantitative relationships in vivo. Several misconceptions that often surround pretargeting are also clarified.