THE lazaroid U-74006F enhances survival of grafted ventral mesencephalic neurons. In this study the intraocular grafting model was used and survival and outgrowth from fetal ventral mesencephalic grafts treated with U-74006F was evaluated in nigrostriatal co-grafts. Fetallateral ganglionic eminence was implanted into the anterior eye chamber and left to mature. Fetal ventral mesencephalon was then implanted and the eyes were treated with U-74006F. The lazaroid treatment enhanced survival of tyrosine hydroxylase (TH)-positive neurons, but did not enhance TH-positive nerve fiber growth into the striatal portions of the co-grafts. However, a marked increasein nerve fiber formation was found within the ventral mesencephalic grafts. Inconclusion, increased cell survival enhanced nerve fiber formation within the ventral mesencephalic portion of the co-graft and not, as expected, in the striatal part.