Areas of striatal grafts which contain neurons that are characteristic of the striatum are called P-zones. We have investigated whether the paucity of P-zones in human xenografts of lateral ganglionic eminence (LGE) tissue in a rat model of Huntington's disease is due (i) to an absence of the appropriate target cells of LGE neurons or (ii) to the persistence of an immature morphology. Striatal tissue from human embryos of varying sizes (21, 24, and 30 mm in crown-to-rump length) was grafted into the ibotenate-lesioned striatum of immunosuppressed rats, which were killed after 15-17 weeks. In most cases, tissue from the LGE and medial ganglionic eminence (MGE) was transplanted together, whereas some rats received grafts of only LGE tissue. Both types of grafts exhibited positive immunostaining for PCNA (proliferating cells), Vimentin (immature astrocytes), and GAP-43 (outgrowing fibers), which indicates that graft maturation is still ongoing up to 4 months after grafting. Graft survival seemed better when MGE was cografted with LGE, suggesting that the MGE may provide trophic support for LGE neurons and can affect the overall survival of human striatal xenografts. However, the extent of P-zone formation was not increased in MIXED, i.e., LGE plus MGE, grafts.