Amnesic patients perform poorly on explicit memory tests that require conscious recollection of recent experiences, but frequently show preserved facilitations of performance or priming effects on implicit memory tasks that do not require conscious recollection. We examined implicit memory for novel visual objects on an object decision test in which subjects decide whether structurally possible and impossible objects could exist in three-dimensional form. Patients with organic memory disorders showed robust priming effects on this task---object decision accuracy was higher for previously studied objects than for nonstudied objects---and the magnitude of priming did not differ from matched control subjects or college students. However, patients showed impaired explicit memory for novel visual objects on a recognition test. We argue that priming is mediated by the structural description system, a subsystem of the perceptual representation system, that operates at a presemantic level and is preserved in amnesic patients.