Among year-before-last beginners ("initiates") of specific substance use, just over two-thirds of crack cocaine, inhalant, and heroin initiates did not use the drug in the past year. Alcohol and marijuana were the only substances for which the majority of year-before-last initiates used the substance in the past year. More than one-tenth (13.4 percent) of year-before-last heroin initiates were dependent on heroin in the past year, and 9.2 percent of year-before-last crack initiates were dependent on any type of cocaine in the past year. Among year-before-last initiates of alcohol use, 25.7 percent had not used alcohol during the past year; 71.1 percent had used alcohol in the past year but were not dependent on it; and 3.2 percent were both using and dependent on alcohol during the past year. Among year-before-last initiates of marijuana, 42.4 percent had not used marijuana during the past year; 51.8 percent had used marijuana in the past year but were not dependent on it; and 5.8 percent were both using and dependent on marijuana in the past year. The NSDUH defines substance dependence according to the criteria specified by the fourth edition of the diagnostic and Statistical Manual of Mental Disorders. It includes such symptoms as withdrawal, tolerance, unsuccessful attempts to cut down on use, and continued use despite health and emotional problems caused by the substance. 2 figures, 1 table, and 7 notes