Although still very preliminary, these studies exemplify how metabolic brain measurements can address questions of relevance in the investigation of drugs of addiction such as: 1. Mechanisms of drug toxicity, i.e., vascular pathology demonstrated from chronic use of cocaine. 2. Neurotransmitters that may be involved in the pharmacological actions of drugs, i.e., alcohol and the benzodiazepine-Gaba receptor complex, marijuana, and the cannabinoid receptor. 3. Mechanisms of drug withdrawal, i.e., hyperresponsivity of the brain to alcohol in the alcoholic, possibly as a consequence of increased sensitivity of the benzodiazepine-Gaba receptor complex. 4. Knowledge about brain function, i.e., the relation between activation of the cerebellum by marijuana and alcohol and the mood-changing effects of these drugs, suggests that the cerebellum may play a role in the mood disturbing actions seen with these drugs (a role which is different from the classical one which associates the cerebellum to motor regulation). Future work will provide more definitive answers to the above questions and will similarly provide information about mechanisms of toxicity, addiction, withdrawal, and reinforcement of other drugs of abuse.