In an acute toxicity study, male and female Sprague-Dawley rats (2 males and 3 females/group, except highest-dose level group which had 4 males and 1 female) were given single gavage exposures to maleic anhydride (as a 10% solution/suspension in corn oil). Dose levels of 316, 398, 501, and 631 mg/kg resulted in the deaths of 0, 1, 3, and 4 animals, respectively (duration of observation period was not reported although the survival time was reported to be one to four days). The LD50 is 495 (410 to 580) mg/kg. Toxic symptoms observed included loss of appetite, diarrhea, and increasing weakness. Gross pathology observed at autopsy included renal and liver congestion, and inflammation of the gastric mucosa.