Smoking is perceived by users to be safer than intravenous injection, but the safety is somewhat illusionary. In addition, the willingness of many people to smoke drugs had a major role in the emergence of the crack cocaine epidemic of the 1980's. Smokable drugs enter the bloodstream rapidly through the lungs and can produce an intensive effect that can be qualitatively different from the drug's steady-state effect. Most cocaine abusers who smoke cocaine use free-base cocaine. The form of free base called crack has become the most popular form of smoked cocaine in the United States. Various forms of cocaine are often mixed with marijuana, tobacco, and PCP. Most PCP users mix it with parsley, tobacco, or marijuana. Methamphetamine can be smoked in one of several ways. Smoking heroin is a dominant form of opiate use in Asia and also occurs in the United States. Opium smoking also occurs in the United States and England. Drug abusers also smoke or inject stimulant and opiate combinations. Future research in pyrolytic chemistry should examine both street drugs and drug combinations; much of the current toxicity information is based on case reports that lack adequate analysis of the drug. The role of cigarette smoking in drug abuse relapse also needs systematic study to determine whether smoking cessation should be part of drug treatment. Table, figure, and 4 references