This paper describes data collection procedures for the part of the New York City Infant Day Care Study concerned with day care environment and caregiver-child interaction. This study is a 5-year, longitudinal investigation in which infants in group and family day care programs and infants reared at home are compared. Study data will be collected from two major sources: (1) observation of each child in his/her usual day care environment (at 6-month intervals), and (2) interviews with the child's caregiver(s) (once a year). The systematic observation and recording of aspects of the behavior of both the child and the caregiver are described as they occur during a typical day of observation. The child, rather than the caregiver, is the major focus of observation. An annual interview with the caregiver is also described. Both longitudinal and cross-sectional comparisons of the data will be made at three levels of analysis: the global assessment (a superordinate score provided by the Infant Day Care Environment Index--IDCEI), the subscales which comprise the IDCEI, and specific hypotheses. (ED)