Novel arylfluoro-1,4-dihydro-4-oxo-1,8-naphthyridine-3-carboxylic acids have been prepared and their antibacterial activity evaluated. These derivatives are characterized by having a fluorine atom at the 6-position, substituted amino groups at the 7-position, and substituted phenyl groups at the 1-position. The in vitro antibacterial potency is greatest when the 1-substituent is either p-fluorophenyl or o,p-difluorophenyl and the 7-substituent is a 3-amino-1-pyrrolidinyl group. 1-(2,4-Difluorophenyl)-6-fluoro-7-(3-amino-1-pyrrolidinyl)-1,4-dihydro- 4-oxo-1,8-naphthyridine-3-carboxylic acid (38) was found to possess excellent in vitro potency and in vivo efficacy.