PBT2 is a metal protein-attenuating compound that might reduce metal-induced aggregation of mutant huntingtin and has prolonged survival in a mouse model of Huntington's disease. A Comment article notes that the trial was not powered to test efficacy but was implemented successfully to its planned conclusion and the drug safety and tolerability was such that larger efficacy trials can be contemplated. The author suggests that at present, the argument for the plausible efficacy of PBT2 still rests primarily on previous in vitro and in vivo animal research, and the current data do not substantially reinforce or diminish that evidence.