The use and abuse of other drugs by Los Angeles County probationers who use diazepam or cocaine has been studied. The results indicate that although diazepam is frequently used alone, it is more often used in combination with other drugs, particularly phencyclidine, opiates, and methadone. The results also indicate that most cocaine users do not use other drugs in combination with their cocaine, but when another drug is used it is most likely phencyclidine, an opiate, or a sedative hypnotic.