Abstract: Objective: To examine the effects of xenografts of microencapsulated bovine chromaffin cells (BCCs) on the rotational behavior of hemiparkinsonian monkey recipients and determine the content of monoamine neurotransmitters and their major metabolites in the neostriatum in hemiparkinsonian monkeys. Methods: The hemiparkinsonian model in monkeys was induced by a unilateral intracarotid injection of methyl-phenyl-tetrahydropyridine (MPTP).Unencapsulated BCCs,BCCs microencapsulated in alginate-polylysine-alginate (APA) membranes as well as empty m-i croencapsules were grafted into the neostriatum of the hemiparkinsonian monkeys. Results: Following the transplantation the hemiparkinsonian symptoms subsided and the number of rotations induced by apomorphine decreased for up to 7 months in the group of recipients grafted with microencapsulated BCCs,while only a temporary improvement (1~2 month) was detected in the recipients of the unencapsulated BCCs.No change was observed in the recipients of empty microencapsules.Dopamine and its metabolites were found considerably depleted in the MPTP-lesioned side versus the unlesioned side of the neostriatum in the hemiparkinsonian monkeys (P <0.05).The extracellular levels of them in the right putamen increased markedly 2months and 7months after the transplantation of microencapsulated BCCs as compared to pretransplantation levels (P <0.05). Conclusion: The results clearly indicate that the transplantation of immunoisolated BCCs can improve the parkinsonian symtoms and increase the content of dopamine and its metabolites for long periods of time in hemiparkinsonian monkeys.The method represents a promising aproach to the treatment of PD and merits further studies.