Abstract: 1-Ethyl-6-fluoro-1,4-dihydro-7-(2,6-dimethyl-4-pyridinyl)-4-oxo-3-quinoline carboxylic acid (Win 52,522) or salt thereof, a highly potent antibacterial agent, is prepared by nitrating the corresponding 6-desfluoro compound (Win 35,439) to produce the corresponding 6-nitro compound, reducing the latter compound to produce the corresponding 6-amino compound and converting the 6-amino via its diazonium salt to said 6-fluoro compound (Win 52,522). Comparative in vitro and in vivo antibacterial test data are provided to demonstrate the uniqueness of Win 52,522 as a highly potent antibacterial agent having a broad spectrum of antimicrobial activity.