Trends indicate that inhalers are more likely to switch to intravenous use than intravenous users are to switch to inhaling. Although less significant than the increase in inhalation, other methods of heroin use have doubled since 1988. Drug Use Forecasting statistics for arrestees in the Washington, D.C., metropolitan area testing positive for opiates indicate declining heroin use. For Baltimore City in particular, adult arrests for heroin increased every year between 1985 and 1989 and then dropped slightly in 1990 and 1991. Juvenile arrest referrals for all drugs were up slightly in 1991 after large increases for the previous 3 years. The National High School Senior Survey for heroin prevalence indicated that 1989 was a peak year, followed by a general downward trend. Data on heroin availability and trafficking show that most opium comes from Southeast and Southwest Asia, that South American cartels are attempting to grow opium poppies and manufacture heroin, that heroin's street-level purity in Baltimore is rising dramatically, that the District of Columbia is experiencing a rise in heroin purity levels and a decline in heroin prices, and that highway heroin interdictions by the Maryland State Police have risen every year since 1988. Heroin trend indicators from New York are also noted, as well as difficulties associated with forecasting heroin demand and trafficking trends in Maryland. 4 footnotes, 18 tables, and 3 figures