Fast cyclic voltammetry was used to measure NO and dopamine (DA) simultaneously in rat caudate putamen (CPu) slices. Analysis of electrochemical signals obtained from mixtures of DA and NO showed that subtraction of either the DA or the NO component revealed the contribution of the other component. Application of such data manipulation to signals obtained in CPu slices indicated that DA and NO components contributed to electrochemical signals. Following electrical stimulation (>1 s), site-dependent NO-like signals were observed. Pressure ejection of NMDA yielded a biphasic electrochemical signal. The first phase (lasting 10-20 s) had electrochemical characteristics of DA and was observed only during the first application of NMDA. The second phase developed more slowly, was of longer duration (1-3 min), and had electrochemical characteristics of a mixture of DA and NO. Generation of the NO-like signal by NMDA was antagonised by L-N-monomethylarginine. Pressure ejection of NO into CPu slices caused dose- and site-dependent DA release. More DA was released in the dorsolateral than in the dorsomedial CPu. Pressure ejection of DA did not generate NO. It is concluded that electrically stimulated DA release is not mediated by prior release of NO.