Fifty-one Asian heroin addicts in Laos were matched for sex, ethnicity, and age with 51 opium addicts. All subjects were voluntary patients at a treatment facility for addicts. The two groups were compared for demographic characteristics, past narcotic history, current narcotic use, and readmission within 1 year following discharge from treatment. Heroin addicts took more doses of drug per day, spent more money per day on narcotic drugs, required higher detoxification doses of methadone, and sought treatment much sooner than did opium addicts. The two groups did not differ for duration of narcotic use prior to becoming addicted, or for rate of readmission following treatment. Demographic differences in occupation and employment reflected the urban distribution of heroin addicts, and the mixed urban-rural residence of opium addicts. These data suggest that heroin is not per se more or less apt to produce addiction (i.e., is not more "addictogenic") as compared to opium. The type of narcotic drug also does not appear to be an important factor in determining treatment outcome. However, heroin does appear to be more "pathogenic" than opium, since heroin addicts sought treatment much sooner than did opium addicts. This may have been due to economic factors (i.e., heroin addicts took more doses per day, spent more time in phases of intoxication and withdrawal, and spent less time in the middle phase with work and other coping behaviors). Opium addiction is not a "benign" or "social" form of addiction. In comparison to heroin, however, opium does cost less, requires fewer doses per day, and has a less toxic withdrawal (at least in the initial phase). Moreover, opium apparently takes longer to produce life crises that motivate the addict to seek treatment.