A study of the potential effects of altered patterning of cortisol--a stress-sensitive hormone detectable in saliva, which when elevated can suppress the immune system--among children who attend child care. The study examines the relationship between cortisol patterning across the day and evening and individual caregiving and temperament, as well as the relationship between cortisol patterning and sIgA--a measure of immune function. The study also discusses the implications for child care policy if cortisol elevations are related to suppressed immune function--including the need to weigh the benefits of child care interventions against potentially compromised health in low-income children who may have additional stressors at home, and suggests further research that could explore ways to minimize the stressors of group care to attenuate cortisol elevations and thus prevent any potential negative effects.