This study compares the psychological development of infants who attend a day care center and who are exposed to special procedures designed to facilitate cognitive development with infants raised at home and infants who are placed in custodial group or family day care. Infants are matched with respect to age, sex, ordinal position, ethnicity, and family background. The infants and their families are enrolled when the children are 3 1/2 months old and are followed until they are 13 1/2 months old. All infants are assessed with a special battery of procedures at 3 1/2, 5 1/2, 9 1/2, 11 1/2 months of age. The infants in our nursery are cared for by a group of mature women carefully screened for sensitivity to the psychological requirements of infants. A detailed manual of procedures has been prepared and is used to train the nursery staff. The manual describes, in extremely concrete terms, specific interactional games between adult care-taker and an infant that contain the essential elements of the desired experiences. These procedures are incorporated in a relaxed yet disciplined fashion into the daily care of the infant. To date 36 infants have been or are presently enrolled in our nursery. Finally, the plan to quantify separate dimensions in cognitive, affective, and social development, rather than rely on instruments which yield a general developmental quotient--IQ--should provide an interesting and unique corpus of longitudinal data on normal development in cognition, social behavior, relationship to mother and general affectivity.