Abstract: On June 26, 1992, during start up procedures for a foam operation, approximately 300 gallons of a chemical mixture containing 35 percent methylene diphenyl isocyanate (MDI) were released uncontrollably from a partially open valve on a pressurized tank. The resulting chemical spill resulted in a complete evacuation of the Perlick Corporation plant and resulted in symptoms among exposed workers that included tightness of the chest and soreness of the throat. Employees #1 through #22 were examined, treated, and released at seven Milwaukee area hospital emergency rooms. Employee #9 subsequently developed a partially collapsed lung. Approximately eight of the exposed workers were involved in emergency response activities prior to the evacuation of the plant.