Abstract: A 5-amino-8-methyl-7-pyrrolidinylquinoline-3-carboxylic acid derivative represented by the general formula: ##STR1## wherein R.sup.1 is a hydrogen atom or a lower alkyl group; R.sup.2 is a hydrogen atom, a lower alkyl group, a lower alkanoyl group, a halogenated lower alkanoyl group or a residue of carboxylic acid ester; R.sup.3 is a hydrogen atom or a lower alkyl group; R.sup.4, R.sup.5 or R.sup.6 are each independently a hydrogen atom or a lower alkyl group; or two of R.sup.4, R.sup.5 and R.sup.6 may be taken together to form a --(CH.sub.2).sub.n -group wherein n is 1 or 2, a stereoisomer thereof, or a pharmacologically acceptable salt thereof, the process for preparing these compounds, a pharmaceutical composition comprising an effective amount of these compounds and methods for the treatment of infectious diseases through the administration to patients of an effective amount of these compounds, and intermediates of these compounds are disclosed. These compounds are effective as antibacterial agents.