The research was based on interviews with 27 active drug-market participants operating on the streets of St. Louis, Mo. Snowball sampling was used to locate these individuals. The interviews were semi-structured and conducted informally. They revolved around a basic set of questions that concerned the offenders' experiences with, and knowledge of, street heroin. Findings show that in St. Louis heroin is perceived to be widely available and good value. Its pharmacology appears to compare favorably to crack due to its greater "controllability." Apparently, this has attracted new, younger users in search of a less stigmatizing, snortable high. The quality of street-level retail units is said to have escalated, in part as a function of newly marketed "uncut" black tar. Selling heroin is perceived by some offenders to be lucrative and less sensitive to the spikes and dips in demand associated with crack. Although the demand elasticity for heroin is clearly lower than that for crack, heroin users generally will consume as much as they can afford to buy within the parameters of what they consider to be a safe dose. This is likely to result in increasing tolerance. This factor, along with other assumptions identified in this article, suggests that the demand for high-quality heroin should grow exponentially. 92 references