Fourteen Sprague-Dawley rats were exposed to CO2 laser exhaust that had first passed through smoke-evacuator filters. Six rats breathed laser vapors that were filtered through commercially available, standard production model smoke-evacuator systems. These animals demonstrated pulmonary lesions identical to but qualitatively less severe than those observed in animals breathing unfiltered vapor. Six additional rats were protected by the interposition of a cartridge filter plus an ultra-low penetration air filter, which trapped 0.1 micron particles; the microscopic sections of the lungs of these experimental rats and two control rats were similar in appearance, i.e., no pathological changes were observed.