Chloroacetyl chloride (CAS No. 79-04-9) was evaluated for acute inhalation toxicity in Fischer rats (6/sex/group) administered single whole- body exposures to dynamically-generated (30 L/min) analytical vapor concentrations of 32, 208, 522, and 747 ppm in air for 1 hour. Based on discrepancies between nominal and analytical concentrations, authors conjectured that CAC (in the presence of moisture) degradation products (monochloroacetic acid and HCl) may have contributed to observed toxicity in this study, although these concentrations were not determined. The 1-hour exposures were universally marked by signs of ocular irritation, including squinting and tearing, and by signs of respiratory distress from exposures to 208 ppm and above, including gasping, and labored breathing. During 2-week post-exposure observation, treated animals showed persisting eye squint (208 ppm and above), tearing (522 ppm and above), and labored breathing (522 ppm and above) and progressive irritative or stress-related clinical signs, including urine stained perineums (32 ppm and above), lethargy (208 ppm and above), reddish periocular stains (208 ppm and above), and salivation with reddish muzzle stains (522 ppm and above). Generally, weight lost during Week 1 was regained during Week 2 post exposure. Mortality consisted of 5/6 males and 1/6 females and was consistent with a 1-hour LC50 (by a moving average method of Thompson and Weil) of 660 ppm for males and greater than 747 ppm for female rats. Necropsy of study lethalities revealed lung and nasal tissue congestion or general circulatory collapse (shock). One male lethality and 5/6 female survivors also had bilaterally enlarged adrenals which, with facial and perineal soiling, the study authors attributed to stress.