The purpose of this study was to develop a reliable instrument for observing the behaviors of caregivers in infant day care centers. Identification of custodial and developmental tasks of infant caregivers was accomplished by a review of the relevant literature, narrative recordings of infant caregivers, and verification of the tasks by a panel of experts. Once identified, the task items were operationally defined, assigned codes and validated. The instrument was designed, codes were positioned in check list form, and a recording technique was selected to ensure reliability. Data were collected and analyzed. Results of the reliability sessions indicate that the Behavioral Observation System of Infant Caregivers (BOSIC) is a valid and highly reliable research tool for assessing infant caregiver behaviors. The frequency estimates generated by BOSIC allow accurate assessment of the percentage of time spent on tasks by infant caregivers. (Author/MP)