In vivo voltammetry in the nucleus accumbens of anesthetized rats was used to investigate the time of onset of dopamine uptake inhibition by intravenous cocaine. There is disagreement between behavioral and neurochemical studies concerning the time-course of cocaine effects. Because of the high temporal resolution of voltammetry, the processes of dopamine release and uptake could be temporally separated to make evaluation of cocaine effects on uptake easier to address. Within 4 s after intravenous cocaine administration (1.5 mg/kg) there was significant inhibition of dopamine uptake that reached a plateau in 20 s. The peak heights of electrically evoked dopamine signals were also rapidly increased by cocaine. The signals returned to baseline values within approximately 1 h. In parallel behavioral studies, locomotor activity was significantly increased within 5–6 s following intravenous infusion of cocaine. Here we demonstrate that intravenous cocaine administration begins inhibiting the uptake of dopamine within a few seconds. This is at least 10-fold faster than previous neurochemical estimates. The present findings may contribute to the understanding of the neurobiological mechanisms underlying the early behavioral responses to cocaine.