We present the case of a professional painter who developed pulmonary alveolar proteinosis (PAP) with severe respiratory failure. He required total bilateral pulmonary lavage on two separate occasions, 3 months apart. Quantitative analysis of particles found in lung tissues obtained by open lung biopsies demonstrated the presence of titanium (60-129 million particles of titanium per cm3 of lung tissue). This report extends previous results from animal studies that demonstrated development of alveolar proteinosis in rats following exposure to titanium. It has been proposed that the overwhelming impairment of the normal clearance mechanisms of the lung by particles of titanium is one of the possible mechanisms responsible for the development of this lung disease. We suggest that a similar mechanism occurred in our patient and that titanium should be recognized as a potential cause of PAP in humans.