Dopamine or its vehicle saline was injected unilaterally into dorsal striatum, ventral striatum, or sites outside the striatum in adult male rats. Direction, duration and frequencies of ongoing behaviors were measured. Dopamine injected into any site within the striatum immediately elicited more contralaterally directed behavior than the vehicle injected into the same site. The contralaterally directed behaviors were no longer duration when injected into the dorsal than into the ventral striatum, a result which might reflect regional differences in numbers of dopamine receptors or distribution of efferents. At the doses employed (25 and 100 microgram), dopamine injected unilaterally into the striatum did not induce rotation, stereotyped behavior, or even a significant change in the frequencies of ongoing behaviors; rather, all ongoing behaviors were expressed in a contralateral direction. Thus, the behavioral effects of dopamine in the striatum are best understood as a change in sensory-motor responsiveness.