Trichloroethylene was administered by inhalation, 7 hours daily, 5 days weekly, for 8 weeks, at concentrations of 600, 100 and 0 ppm, to Sprague-Dawley rats and Swiss mice; and for 104 weeks to Sprague-Dawley rats; and for 78 weeks to Swiss and B6C3F1 mice at concentrations of 600, 300, 100 and 0 ppm. The animals were kept under observation until spontaneous death. In the experiments reported herein, 3768 animals were studied. Under the experimental conditions, trichloroethylene appears to be carcinogenic in rats and mice (particularly in male Swiss mice). The most relevant finding was the dose-related increased incidence of Leydig cell tumors in male rats, and the onset of few renal tubuli adenocarcinomas at the highest dose, always in rats (4/130 males and 1/130 females). The renal tubuli adenocarcinomas were preceded by, and associated with, a characteristic lesion of the kidney: tubuli cell karyomegaly (megalonucleocytosis).