Sulfamethoxypyridazine, has been introduced into clinical usage which differs in several respects from currently available preparations of this group of drugs.1 The new agent is promptly absorbed after oral administration, and the free form of the drug is very slowly excreted in the urine. This results in long-sustained high plasma concentrations of free drug with doses much lower than those required to attain similar concentrations with several other sulfonamide agents.