It was proposed that apomorphine and the ergot derivative pergolide induce rotation in 6-hydroxy-dopamine (6-OHDA)-denervated rats by different receptor mechanisms, since these dopamine agonists induce different patterns of rotational behaviour, have different dose-response curves and are differently inhibited by neuroleptics acting on D1 or D2 type receptors. The synaptic continuation of the striatonigral pathway was interrupted in unilaterally 6-OHDA-lesioned rats by adding a kainic acid lesion to the 6-OHDA-lesioned nigra. This lesion affected apomorphine and pergolide rotation differently. After an initial short peak of contralateral rotation, apomorphine induced ipsilateral rotation that increased with dose, although a final contralateral peak was always maintained. The only change in pergolide rotation was a shift of the dose-response curve to the right. In another group of animals, the continuation of the striatonigral pathway was lesioned by unilateral kainic acid injections without previous 6-OHDA-lesions of the dopamine system. In these animals apomorphine but not pergolide induced rotational behaviour. In contrast, both drugs induced rotation in animals where all striatal efferents were lesioned unilaterally by kainic acid injections into one striatum. The results suggest that the apomorphine rotation is mainly dependent upon striatonigral pathways while the pergolide rotation is dependent upon other striatal efferent pathways.