Twenty-three subjects exposed to naphthalene-diisocyanate (NDI, [mean air concentration 0.002-0.007 mg/m3]) were examined with regard to symptoms and pulmonary function. Irritation of the eyes, cough, and exertion dyspnea were more common in exposed subjects than in unexposed controls. Closing volume, as a percentage of vital capacity (CV%), was 6% higher than the reference value (P = .01) on Monday morning after 2 days with no exposure to NDI. The other lung function variables were normal. Two days of industrial exposure caused no further change in any lung function variable. The difference between measured and expected CV% increased with age in the exposed subjects. Five employees who had complained of severe symptoms during NDI exposure and who, therefore, had been transferred to other tasks with no exposure to NDI, displayed marked increases in CV% and a reduction in the forced vital capacity by an average of 0.6 L. Smokers and nonsmokers displayed similar lung function changes.