Amnesia for the events occurring during surgical operations is a desirable feature of general anesthesia but is not always attained. Evidence from research on memory suggests that anesthetic amnesia results from 1) attenuation of sensory transmission and 2) impairment of the ensuing memory-consolidation process. In a few patients, however, auditory information of high emotional content, coinciding with a lightening of anesthesia, results in memory consolidation sufficient to permit unpleasant recall, spontaneously or under hypnosis. The physiologically desirable light levels of modern anesthesia impose the constraint of avoiding conversation in surgery that can result in psychologically undesirable memory traces.