The purpose of this study was to investigate whether or not infants who had experienced different types of naturally-occurring, significant separations from an attachment figure during the first year of life differed in their response to separation at 12 months of age. Thirty-three 12-month-old Caucasian infants from middle class, intact families were divided into three groups on the basis of the frequency/duration patterning of brief, nontraumatic separations from the mother during their first year. One group of infants had experienced separation only when their parents left them occasionally with a babysitter (as for an evening); a second group had experienced one or two separations of relatively long duration (when parents went on vacation); a third group had experienced frequent regularly-scheduled separations of short duration (when mothers worked or attended school). Subjects' response to separation from and reunion with the mother was assessed at 12 months of age. No differences between groups in mean response were found. The data suggest that brief separations from a primary attachment figure need not have deleterious effects if an infant is provided with high-quality substitute care. (Author/MS)