Operant behavior maintained by schedules of intermittent reinforcement has been extensively used for the investigation of the behavioral effects of drugs that affect the central nervous system. While the primary purpose of such research has been the screening of novel compounds in the search for clinically effective drugs, much else has been discovered about drug action and behavioral processes. Current research focuses on problems of social and clinical importance, such as cocaine abuse, and involves the development of novel and modified reinforcement schedules to address problems thrown up by research involving drugs. There are also new challenges posed in studying the behavior of transgenic knock-out mice. After more than 40 years, reinforcement schedules continue to be significant research techniques in behavior pharmacology. It is important that researchers are fully trained in behavior analysis in order to contribute to this rapidly developing area of behavioral neuroscience.