Two experiments were conducted to evaluate the hypothesis that the memory disorders of Huntington's Disease (HD) patients are characterized by deficiencies in both retrieval mechanisms and the acquisition of procedural (skill-based) information. In the first study, verbal recall and recognition tests were administered to HD patients, amnesics and normal control (NC) subjects. Although the two patient groups were impaired relative to NC subjects on both recall and recognition of word lists, the performance of the HD patients was superior to that of the amnesics on the recognition test. In the second experiment early HD (EHD), advanced HD (AHD), amnesic and NC subjects were compared in the acquisition of the 'Tower of Hanoi' puzzle. Both the NC subjects and EHD patients acquired the solution of this puzzle after repeated trials, whereas the AHD and amnesic patients evidenced little improvement. However, on a recognition test assessing memory for facts about the puzzle, both the EHD and AHD patients were superior to the amnesic subjects. These results are consistent with the retrieval hypothesis but are equivocal with regard to the HD patients' proposed deficit in skill learning. Since the 'Tower' puzzle may rely heavily on both problem solving and skill learning capabilities, it may be of limited value in searching for double dissociations between patient groups and the acquisition of skill-based and data-based knowledge.