Diftalone is a symmetrical tetracyclic compound with anti-inflammatory and antipyretic activities. The anti-inflammatory potency of diftalone is greater than that of aspirin, approximately equal to that of phenylbutazone, but lower than that of indomethacin. Diftalone exhibited limited but statistically significant antipyretic activities. It less potent than aspirin or phenylbutazone. Diftalone seems to be an effective and safe anti-inflammatory agent in the treatment of rheumatoid arthritis. It demonstrated the same activity as indomethacin and phenylbutazone. However, because of hepatotoxicity and carcinogenicity (hepatoma) in preclinical studies and hemotoxicity and gastrointestinal adverse effects in humans, diftalone was withdrawn by its manufacturer.