A carbon fiber microelectrode is shown to give a potential-dependent dopamine-selective response in rat brain tissue. However, distinct evidence for dopamine release is not obtained with intraperitoneal amphetamine administration (1.8 or 3.7 mg . kg-1). In rats which have been unilaterally depleted of dopamine, the change in electrochemical signal obtained in the lesioned striatum is very similar to that measured on the non-lesioned side following amphetamine administration. This indicates that substances other than dopamine contribute to the observed signals.