The National Institute for Occupational Safety and Health (NIOSH) requests assistance in preventing asthma, other respiratory diseases, and death from exposure to methylenebis(phenyl isocyanate) (MDI). More than 10,000 U.S. workers are potentially exposed to MDI during spray-on truck bed lining operations. This Alert summarizes four case reports: one death and several incidents of asthma or other respiratory disease following exposure to MDI during spray-on truck bed lining operations. Information about preventing adverse health effects from exposure to MDI is urgently needed by workers, employers, small business owners, and physicians and other health care providers. *MDI is methylenebis(phenylisocyanate). In this fact sheet, MDI refers to all MDI-based isocyanates.