Changes in homovanillic acid concentration, recorded in vivo by voltammetry with carbon-paste electrodes, were used as an index of dopamine release. With electrodes implanted in frontal cortex, nucleus accumbens and striatum, the pattern of dopamine release was monitored simultaneously in the three brain regions together with the rats' motor activity. Changes in response to the systemic administration of dopamine-receptor agonists and antagonists were used as an index of feedback control of dopamine release. The relationships between dopamine release and motor activity, as well as that between dopamine release in the different brain regions, were investigated by calculating correlation coefficients for data collected over 24-h periods. The results show that dopamine release in frontal cortex is subject to little feedback regulation, that there is no nocturnal increase and no correlation with motor activity. Dopamine release in accumbens and striatum follows a very different pattern. There was a high correlation between dopamine release in these two regions on both sides of the brain; the correlation between the accumbens and the ipsilateral striatum was the highest. Dopamine release in both regions shows evidence of considerable feedback regulation, a nocturnal increase and a high correlation with motor activity. The importance of the accumbens in relation to the level of motor activity is supported by the finding that the correlation coefficient between motor activity and dopamine release in this structure was significantly higher than that between activity and release in the striatum.