Recent conflicting findings raise the issue of whether observed differences in levels of psychological distress of 1st and later borns are a function of their contemporary social situation, or of basic personality defect in 1 or the other group. Hypotheses which might explain conflicting findings are derived from Schachter''s work: among Ss exposed to stressors, 1st borns will show more symptoms when social isolation is enforced, and later borns when social interaction is enforced. These hypotheses are tested in a socially isolating sensory deprivation study, and in a community sample including crowded slum dwellers. Both hypotheses are supported.