One of the fundamental goals of neuroscience is an understanding of the relationship between neurotransmission and behavior. Although considerable information has come from methods such as push-pull perfusion, obtaining data about neurotransmitter release in behaving animals has been quite difficult. Recently voltammetry, a standard electroanalytical technique, has been shown to be applicable to monitoring the extracellular neurochemistry of monoamines and related compounds. Since the original report from the laboratory of R.N. Adams (Kissinger et al., 1973), more than 100 papers have been published on in vivo voltammetry and its application to the study of monoamines in the central nervous system. (1982) and (1983) have recently reviewed the subject. Because of the complexity of the extracellular environment of the brain, most of the work to date on in vivo voltammetry has addressed the issue of interpretation of the data rather than the application of the technique. As the interpretation of in vivo voltammetric data has clarified, applications have started to appear that clearly demonstrate the utility of the method for obtaining new information about monoamines in vivo.