Weekly observations of two normal children in their own homes were carried out during the period from birth to the second birthday. Narrative observations were coded and computer processed to yield ‘patterns of experience’. These summarize for a given time span in the child’s life the frequency with which he showed certain behavior and/or the frequency with which events to which he was responsive occurred in the environment. Numerous other data, including a variety of developmental scales, were collected concerning the same subjects and their families. For each child behavior and experience were compared at times when mother was in direct interaction with the child, and times when the infants were in contact with other persons (usually fathers and relatives) while mother was at a distance. It is shown that mother’s close proximity had a marked impact upon the behavior of each child in all areas, but the direction of the effect was opposite. One child decreased responsiveness and activity in all spheres in mother’s absence; the other increased responsiveness and activity as if to fill a void. This difference is discussed in the light of differences in the development of the mother-child relationship in the two cases. The material is used to illustrate the contribution an ecological approach to infant behavior can make to a sharper understanding of mother-child interactions and their role in shaping cognitive as well as personality development during the first few years of life.