The occurrence of hemoptysis, dyspnea, and bilateral pulmonary opacities progressed to respiratory failure in a 34-yr-old man. Recovery occurred with corticosteroid therapy. In the absence of evidence for an infectious etiology, the possibility of immunologic trimellitic anhydride (TMA) hemorrhagic pneumonitis was considered when the lung biopsy excluded Goodpasture's and other diseases and because the patient was a spray painter. Serologic evaluation for antibodies against TMA was requested. Because the immunologic studies for TMA were negative, and because the patient was a spray painter, immunoassays for three isocyanates conjugated to human serum albumin (HSA) were carried out although there was no specific history of isocyanate exposure at that time. High levels of IgG and IgE antibodies were detected against hexamethylene diisocyanate (HDI)-HSA and toluene diisocyanate (TDI)-HSA. Further investigation documented exposure to spray paint that contained HDI and another isocyanate. The paint was sprayed on warm metal, and subsequently the worker developed an acute illness. Further plant studies were not possible. We propose that the pathogenesis of this case of hemorrhagic pneumonitis is immunologic because of uncontrolled exposure to HDI and TDI, is analogous to the immunologic hemorrhagic pneumonia caused by TMA, and should be considered as a possible cause of a similar acute lung disease after isocyanate exposure.