This experiment investigated the durability of implicit memory for a single episode in normal and amnesic subjects. The target materials consisted of sentence puzzles that were difficult to comprehend in the absence of a key word or phrase. Sentences were re-presented at delays ranging from one minute to one week, and implicit memory was indicated by facilitation in solving previously incomprehensible sentences on subsequent exposures. Patients with severe memory impairments on tests of explicit recall and recognition showed substantial and robust facilitation, or priming, from a single prior presentation and there was no evidence of a systematic decay of facilitation over retention intervals up to one week. The long-lasting implicit memory observed in the sentence puzzle task contrasts with previous findings of rapid decay of priming effects in amnesic patients.