The research reported in this symposium paper attempts to underline a Piagetian distinction concerning object concept which has tended to be ignored by psychologists working along Piagetian lines. More specifically, this research tested the hypothesis that intellectual development plays a role in the development of stranger reactions. The subjects were 32 middle-class infants from 31-57 weeks of age, with four boys and four girls in each of the four age groups averaging 32, 40, 48, and 56 weeks. The observed behavior of the infant in the presence of a stranger was classified into three main categories; positive, negative, and mixed reactions. Responses were coded +, -, or 0 along the following dimensions: fine and gross motor activity, facial expression, and vocal behavior. The comparison between the results obtained on the human object scale and on the causality scale were coherent with Piaget's theory, which holds that the premanency of the object is the fundamental concept which determines the notions of space, causality, and time. (CS)