Mother-infant interaction characteristics at six ages during the first year of life were studied in relationship to the development of the infant's fear of strangers (FOS) during the first year. Among 46 offspring of women with psychosis history, a failure to develop the expected FOS was associated with antecedent negative qualitative aspects of interaction such as increased maternal tension, reduced harmony in feeding and increased infant crying. Among 80 low-risk control infants, a failure to develop FOS was associated with an antecedent quantitative reduction in social contact within the mother-infant pair. At a case level, an absence of FOS overlapped little with anxious attachment to the mother, and these two developmental phenomena bear partially different relationships to the mother-infant interaction characteristics.