Four out of five narcotic addicts among both black and white subjects reported some use of nonnarcotic drugs during their careers. Overall, marijuana and cocaine were by far the most widely used drugs. Barbiturates were also popular, particularly among white addicts. Amphetamines and hallucinogens were mentioned by at least one-fourth of the white addicts and much less frequently by blacks. Among addicts of both races, cocaine and barbiturates were much more prevalent during addiction periods than during nonaddiction periods. Among white addicts, but not among blacks, marijuana, benzodiazepines, and hallucinogens were considerably more popular during non addictive periods than during addiction periods. Narcotic use may be exacerbated by an interactive or catalytic effect of narcotic and nonnarcotic drugs. Apparently nonnarcotics complement and substitute for narcotic drugs during addictive and nonaddictive periods. 2 data tables and 7 references.