Historically, most investigations of the social and psychological effects of disaster have focused on describing the impact of single traumatic events rather than on developing an understanding of how disasters or particular characteristics of disasters affect various groups of victims. This study investigated the hypothesis that stress caused by a technological disaster would be higher months after the incident than stress following a natural disaster. Levels of stress and feelings of helplessness were compared for three subject groups: (1) 27 residents of a community immediately adjacent to a leaking toxic waste dump; (2) 23 residents of a community which had been flooded; and (3) a demographically similar comparison group (n=27). Stress was measured using the Symptom Checklist: 90R (a self-report measure of emotional and physiologic distress), a proofreading task as a performance measure, and analyses of urinary catecholamines measuring physiological arousal. Questionnaires of life events, demographics, and background characteristics were used to control for other sources of stress. The results revealed that residents of the landfill neighborhood exhibited higher levels of stress across self-report, behavioral, and biochemical domains of measurement than did residents of either the flood neighborhood or the comparison neighborhood. These landfill residents also reported feelings of helplessness more frequently than did flood victims or the comparison group. Although this disaster study was essentially a case study, the hypothesis that technological disasters are more likely to cause chronic stress than are natural disasters was supported. (ABL)