A microtransplantation approach has been used in order to achieve more complete reinnervation of the dopamine denervated rat striatum by fetal nigral cell suspensions injected into multiple striatal sites. A total of 450,000 cells, obtained from the ventral mesencephalon of embryonic day 14 rat fetuses, were implanted either in the conventional way as two 1.8-microliters deposits centrally in the head of the caudate-putamen ('Macro grafts'), or as eighteen 0.2-microliter deposits disseminated over six needle penetrations in the same area using a 50-70 microns glass capillary tip ('Micro grafts'). Non-grafted lesioned rats served as controls. Dopamine neuron survival (as assessed by tyrosine hydroxylase immunohistochemistry at 4 months after transplantation) was 2.8-fold greater in the Micro grafts as compared to the Macro grafts. Striatal dopamine tissue levels (determined in a separate group of rats) was increased 2.5-fold in the head of the caudate-putamen (from 12.5% of normal in the Macro graft group to 30% of normal in the Micro graft group). Consistent with this, the overall graft-derived tyrosine hydroxylase positive fiber outgrowth was more extensive in the Micro graft group and covered larger areas of the previously denervated caudate-putamen. The results show that distribution of the fetal nigral tissue in multiple small deposits provides for increased dopamine neuron survival, probably because of a closer contact between the implanted cells and the surrounding host striatal tissue in the small-sized graft deposits. Less bleeding and necrosis at the implantation site may also have contributed to this effect. The present microtransplantation procedure is an efficient means to increase overall dopamine neuron survival and to achieve more complete reinnervation of the denervated striatum in the rat Parkinson model. It also substantially increased the reproducibility of DA graft survival between animals.