Previous quantitative and qualitative structure-activity studies in antibacterial monosubstituted l-ethyl-1, 4-di-hydro-4-oxoquinoline-3-carboxylic acids prompted us to synthesize the 6, 7, 8-polysubstituted compounds. In this paper, the preparation and antibacterial activity of the 6, 7-and 7, 8-disubstituted compounds and their derivatives are described. Among these compounds, l-ethyl-6-fluoro-1, 4-dihydro-4-oxo-7-(l-piperazinyl) ...