This longitudinal study of 10 infants in a day care nursery traces the development of recognition and attachment to a primary caregiver from approximately 3 1/2 months of age (shortly after enrollment in the program) through the end of the first year. Monthly assessments of about 10 minutes each, on two successive days, were made of the infant's recognition of and attachment to their primary caregivers. Examined were infant responses to the approach of the caregiver as compared to the approach of a stranger, responses to the mother's departure when the infant was left with the caregiver as compared to being left with a stranger, and the infant's response to being left with a stranger by the caregiver as compared to being left with a stranger by the mother. Results indicate that: (1) as the child grows, the response to a stranger becomes increasingly less positive when compared to response to the caregiver, which remains neutral; (2) infants' response to their mothers leaving them with a stranger show increasing evidence of distress, starting at 7 months and increasing, while infants continue to remain generally comfortable when left with the caregiver; (3) around 6 to 7 months of age, infants show equivalent negative reactions when being left with a stranger by either the mother or the caregiver. A discussion reviews the results in relation to day care services. (SB)