The model is based on the idea that the behavior of the heroin system in the United States is affected primarily by how much heroin is available at any given time (inventory) and the amount drug addicts want (demand inventory). The ratio between inventory and demand inventory is referred to as the Relative Abundance Measure. The model forecasts the drug user population, drug purity, drug prices, and drug-related deaths. Sources and amounts of heroin imports used in the model correspond to sources and amounts commonly accepted by various agencies concerned with drug abuse. Additional research is recommended to evaluate the model's effectiveness and reliability and to explore potential model applications. 5 references, 1 table, and 12 figures