Environmental illness is an increasingly frequent and medically unexplained syndrome of "allergy" to common environmental agents. A recent outbreak of chemical-induced illness allowed study of psychological factors in environmental illness. Thirty-seven symptomatic plastics workers completed structured diagnostic interviews and self-report measures of somatization and psychopathology. The 13 subjects who developed environmental illness scored higher on all measures than those who did not. The greatest differences were in prior history of anxiety or depressive disorder (54% versus 4%) and number of medically unexplained physical symptoms before exposure (6.2 versus 2.9). These findings suggest that psychological vulnerability strongly influences chemical sensitivity following chemical exposure.