Four to six weeks following unilateral striatal kainic acid (KA) lesions, challenge with apomorphine (0.5-0.75 mg/kg s.c.) elicited rotational behavior. Gestational day 17-19 rat fetal striatal tissue was implanted into the lesioned striatum, and rats were rechallenged with apomorphine 10 weeks post-transplant. There was a significant reduction in the maximal rate of rotations and an alteration in the topography of locomotor activity in response to apomorphine. These data indicate that the transplanted material may possess similar pharmacological properties as the original host tissue and is capable of functionally repairing damage to a complex neurochemical system.