Cyanuryl chloride (CAS No. 108-77-0) was evaluated for acute inhalation toxicity. The test substance was administered via inhalation to male and female albino rats of the Tif: RAIf (SPF) strain for 4-hours. Concentration levels and mortality data are as follows: 0.0 (0/10 M, 0/10 F); 5.0 (0/9 M, 0/9 F); 7.0 (0/9 M, 0/9 F); 18.4 (1/9 M, 0/9 F); 40.5 (6/9 M, 0/9 F); 108 (9/9 M, 6/9 F); and 495 mg/m3 (9/9 M, 9/9 F). Clinical signs included a dose- related increase in dyspnea, chromodacryorrhea, rhinorrhea, cyanosis, diarrhea, tremors and ruffled fur as well as lateral, ventral, and curved body position. A significant decrease in body weights was noted in both sexes at 40.5 mg/m3, and depressed body weights and weight gains at 108 mg/m3. Pathological findings revealed an area of discoloration of the lungs in all exposure groups. At 40.5 mg/m3, enlarged or edematous lungs in 6/9 males was present, and similar findings were noted in 7/9 males and 6/9 females in the 495 mg/m3 group. Also noted was dilation of the stomach in 1 male in the 108 mg/m3 groups and 1 animal of each sex in the 495 mg/m3 group. The LC50 for males was 35 mg/m3, and for females was 88 mg/m3. The test substance was determined to be very toxic when administered to rats by the inhalation route.