Four non-steroidal anti-inflammatory agents have been determined titrimetrically using N-bromosuccinimide. Flufenamic and mefenamic acids react quantitatively with N-bromosuccinimide in an acidic medium whereas allopurinol and indomethacin can be determined with reproducible results in an aqueous pyridine solution. The method has been successfully applied to the determination of flufenamic acid, mefenamic acid and allopurinol in their pharmaceutical formulations. In addition, a sensitive spectrophotometric method, based on the same reaction, has been used to determine selectively indomethacin in admixture with its hydrolysis products, and for the determination of indomethacin in capsules.