This paper focuses on the role of research in assessing what impact changes in the supply of heroin from source countries might have. Such changes are difficult to explain and even harder to predict due to the lack of reliable data on drug production, price indices and a range of other variables. This paper reviews lines of heroin supply, up to the borders of drug consuming nations. It argues that the descriptive method most regularly used to present supply indicators needs to be supplemented with a conceptual approach. Theories or models of drug supply are required in order to advance research, improve empirical collections and broaden knowledge about drug markets in general.