Rats inhaled a paste polymer polyvinyl chloride dust at an aerosol concentration of 10 mg/m3 for 6 hr/day, 5 days/wk for a 15-wk period. A small number of randomly scattered lung lesions were detected at 15 wk; these lesions were also present 15 wk after exposure to polyvinyl chloride had ceased. Few if any biochemical changes were detected at the alveolar surface in lung tissues or other organs of polyvinyl chloride-exposed rats. It is therefore concluded that at "nuisance" dust level this form of polyvinyl chloride polymer exhibits a weak biological reactivity.