The model allows government authorities to track, and react to, fluctuations in the heroin market, and provides insight into how fundamental factors affecting the behavior of the heroin system are interrelated. The model provides a general structure that may be applicable to trafficking patterns in other illicit drugs. This article discusses the model's ability to predict the size of the heroin addict population in the U.S. as one means of demonstrating the model's validity. Three areas where data are available to compare to model-generated numbers include heroin purity, heroin price, and heroin-related deaths. 1 table, 12 figures, 2 notes, 6 references, and 1 appendix