In an original form of delayed response experiment which affords the subject opportunity to select from among 4 food boxes the 1 previously seen baited the ability of chimpanzees to respond correctly with immediacy and apparent ease after delays of at least 3 hrs. has been demonstrated by the authors. Four subjects were used, ranging in age from approximately 4 to 71/2 yrs., 2 of each sex. It was further discovered (1) that the original location or position of the food container ordinarily determined response; (2) that mnemonic response to a constant visual datum, such as color, is possible after a delay of at least 30 min. when dependence on absolute or relative position of the food container is rendered impossible. When color is the sole indicator, the observational carelessness and immediacy of response which appeared when position or location could be depended on were replaced by hesitation, observational scrutiny, comparison, vacillation, recognition. When the subject, having selected the position where it had previously seen the food placed, discovered there an empty container, it frequently expressed disappointment, incredulity, mystification, resentment, anger, depression, and, in a few instances, refused to continue to work. Demonstration of mnemonic response to experimentally varied and simplified situations in which only one conspicuous sensory feature, for example color, remains constant, undoubtedly is the most important result of this investigation. Memory for persons in the chimpanzee, after intervals of at least 10 mos., and of the presence and location of buried food after delays of 48 hrs., also was demonstrated. The results reveal pronounced individual differences in temporal span of memory, and also marked superiority of [female] over [male].