Antimicrobial lactam-quinolone compounds comprising a lactam-containing moiety linked to a quinolone moiety, of the formula: ##STR1## wherein (1) A.sup.1, A.sup.2, A.sup.3, R.sup.1, R.sup.4 and R.sup.6 generally form any of a variety of quinolone, naphthyridine or related cyclic moieties known in the art to have antimicrobial activity; and(2) R.sup.1 or R.sup.3 contain a linking moiety, linking the quinolone moiety to a lactam-containing moiety having the formula: ##STR2## wherein (3) R.sup.10, R.sup.11, R.sup.12, R.sup.13, and R.sup.14, together with bonds "a" and "b", form any of a variety of lactam-containing moieties known in the art to have antimicrobial activity; and(4) the linking moiety includes (for example) carbamate, dithiocarbamate, urea, thiourea, isouronium, isothiouronium, guanidine, carbonate, trithiocarbonate, reversed carbamate, xanthate, reversed isouronium, reversed dithiocarbamate, reversed isothiouronium, amine, imine, ammonium, heteroarylium, ether, thioether, phosphono, phosphoramide, phosphate, sulfonamide, ester, thioester, amide, and hydrazide groups.