Residents of an area near a hazardous toxic waste dump and a matched control area 5 miles from any toxic storage site were compared to examine mediation of chronic stress by feelings of uncertainty and helplessness. Self‐report, behavioral, and biochemical measures of stress were collected and were analyzed as a function of whether subjects lived near the toxic hazard as well as in light of feelings of uncertainty and helplessness. Subjects living near the landfill were concerned about the hazard, reported more symptom distress, performed more poorly on a task requiring concentration and motivation, and exhibited higher levels of urinary catecholamines than did control subjects. Feelings of uncertainty were only modestly related to stress, but helplessness was more central to chronic stress among people living near the hazard.