The development of object permanence was investigated in a longitudinal study of two infant rhesus monkeys in a human analogue testing situation and two subhuman analogue testing situations. The ages at which certain object-related behaviors were demonstrated by the subjects as stable responses were found by the presentation of tasks that involved various manipulations of objects. In each testing situation was found a sequence of development of object permanence that was very similar to the one described by Piaget for the child, and in each case the sequence culminated in behaviors nearly as complex as those described by Piaget for the 2year-old human infant. Piaget (1954) outlined the child's progression to a concept of object permanence. He described a developmental sequence composed of six stages culminating when the child is approximately 2 years of age. This description was derived from observations of the behaviors of his three children in relation to objects that were made to disappear in different ways. Some longitudinal and cross-sectional studies have supported Piaget's description (Gorman & Escalona, 1969;Gouin Decarie, 1965). Other investigators have considered the effects of variables such as attention and memory (Miller, Cohen, & Hill, 1970), perceptual processes (Bower, 1967), environmental background (Golden & Birns, 1968, and specific experience (Landers, 1968) on object permanence.In two recent studies (Gruber, Girgus, & Banuazizi, 1971;Vaughter, Smotherman, &