Abstract The synthesis and antimicrobial activity of 5-Hydroxy-l-ethyl-1, 4-dihydrio-4-oxo-3- quinolinecarboxylic acids and their derivatives have been investigated. The 5-hydroxy-3- quinolinecarboxylic acids were prepared by thermal cyclization of 3- oxocyclohexenylaminomethylenemalonates followed by aromatiza-tion with iodine-ethanol, ethylation and hydrolysis of products. The 5-amino derivatives were prepared by several ...