Chronic toxicity was evaluated in groups of 120 (60 male, 60 female) CD rats and Syrian hamsters exposed to nominal concentrations of 0, 200, 600, or 2000 ppm tetrafluoroethylene vapor (purity not reported) 6 hrs/day, 5 days/week for approx. 90 days. The following statistically significant clinical effects were observed in rats: lower mean body weights during most of the study, and lower overall body weight gains for male and females at 2000 ppm; higher incidence of alopecia and sores for animals in the 2000 ppm group; exposure related increases in urinary fluoride levels in males and females; increased urine volume in females exposed to 600 or 2000 ppm TFE with accompanying decreases in osmolality in the 200 and 2000 ppm groups; and decreased creatinine in all treated females. The only significant clinical observation reported in hamsters was an increase in the frequency of ocular abnormalities (scabs over eyes) in females exposed to 600 or 2000 ppm TFE. Rats showed the following significant blood related effects: a decrease in the serum albumin/globulin ratio at 45 days in all treated females; decreased serum albumin in 600 and 2000 ppm females at 45 days, and in 2000 ppm females at 90 days; elevated serum glutamic-pyruvic transaminase activity in femalesexposed at the 2000 ppm level; decreased hematocrits in 200 and 2000 ppm male rats, with decreased mean corpuscular volumes in 2000 ppm male rats; and temporarily elevated leukocyte counts in the 600 and 2000 ppm female rats. The only significant hematological effect reported in hamsters was a decrease in serum albumin in 2000 ppm males at 90 days. Following necropsy, significant observations in rats included a dose related increase in kidney and liver weights at the 2000 ppm level, and tubular nephrosis of the straight portions of the proximal convoluted tubules in animals exposed to 600 or 2000 ppm TFE, observed at 45 and 90 days. Observations in hamsters included a dose related increase in mean relative liver weights in females; and atrophic changes in immature or mature testes of hamsters exposed to 2000 ppm TFE.