This paper reviewed heroin use data from the US government's epidemiologic monitoring system for substance abuse. The monitoring system has multiple components, i.e., the Drug Abuse Warning Network of reporting emergency rooms (9), annual surveys of high school and post-high school youth (3, 4), annual National Household Surveys of Substance Abuse (7, 8, 50), Drug Use Forecasting (51), the Community Epidemiology Work Group (52), and law enforcement systems not reviewed here. These monitoring systems should identify any major increase in heroin incidence in this country relatively early. This is important, because the early stages of heroin epidemics are often hidden from society, and the epidemics are already full-blown by the time health and other agencies become aware of the size of the affected population and are required to respond. The hidden or underground nature of heroin epidemics is caused by 1) the need of each user to hide an illegal activity and 2) the delay between the time when heroin is first used and the onset of physical dependence and other adverse consequences, which bring new heroin addicts to the attention of treatment and enforcement systems. Despite an epidemiologic surveillance system which should rapidly identify large-scale heroin spread in this country, our treatment and law enforcement systems are not organized to respond rapidly to contain an epidemic. Substance abuse treatment services are not structured for rapid expansion and contraction based on fluctuating need. Apart from HIV prevention programs, we do not have outreach teams attached to treatment programs that could quickly identify local outbreaks and involve new heroin abusers in treatment (10).(ABSTRACT TRUNCATED AT 250 WORDS)