A new series of quinolone derivatives 3a--1 bearing 3-amino-4-methoxypyrrolidines of different configurations and chirality were synthesized and their antibacterial activities as well as some of their toxicological properties were examined. As predicted by our previous quantitative structure-activity relationships (QSAR) analysis of C-7 heterocyclic amine substituted quinolonecarboxylic acid antibacterial agents, these pyrrolidine derivatives showed higher in vitro and in vivo antibacterial activities against both gram-positive and gram-negative bacteria than the analogs bearing various 3-substituted azetidines. Furthermore, the amino and methoxy substituent groups on the pyrrolidine ring exhibited strong configurational and chiral effects on the in vitro and in vivo antibacterial activities of these compounds: (1) cis compounds showed higher antibacterial activities against most of the pathogens examined; (2) N-methylation of the 3-amino group on the pyrrolidine ring lowered in vitro but not in vivo antibacterial activities, particularly leading to superior in vivo anti-pseudomonal activity; (3) the (3'S,4'R)-derivative showed substantially higher activity that the (3'R,4'S)-one. These findings led to the selection of compound 3k for further evaluation as it possessed the highest in vivo antibacterial activity and no cytotoxicity.