Inhalation exposure of guaranteed reagent grade trichloroethylene was performed in female ICR mice and female SD rats at 50, 150 and 450 ppm for 7 hours a day, 5 days a week, for 104 weeks followed by an observation period of 3 weeks. Tumors were distributed mainly in the hematopoietic systems, lungs and mammary glands in the mice, and in the pituitary glands and mammary glands in the rats, while several types of tumors were observed in other organs at low inci-dences. The average number of lung tumors per mouse in mice exposed to 150 ppm or 450 ppm was more than 3-fold the incidence in control mice. The incidences of pulmonary adenocarcinomas in mice exposed to 150 ppm and 450 ppm were 16% and 15%, respectively, which was significantly (p<0.05) higher than that of the controls (2%). No significant differences in the incidences of other types of tumors, tumors of specific organs by site of origin or numbers of animals with tumors were recognized between the controls and dosed groups of mice and rats.