Studies in Parkinson's disease using the Core Assessment Program for Intracerebral Transplantation (CAPIT) protocol have demonstrated that grafts of embryonic mesencephalic cells into striatum can survive, grow, and exert useful clinical effects. Attention in now being directed toward neural grafting in other conditions, such as Huntington's disease. As a precondition for grafting of embryonic striatal cells into diseased striatum in this complex motor and psychiatric disorder, not only is further basic research needed, but also a thorough and wide-ranging assessment protocol is essential. This article presents such a CAPIT-HD assessment protocol.