4-dihydro-7-(3-hydroxypyrrolidin-1-yl)-4-oxoquinoline-3-carboxylic acid (10) were prepared. One of the isomer, 7-[(3S)-hydroxypyrrolidin-1-yl] derivative 8, was about 4 times more potent in vitro than the other, 7-[(3R)-hydroxypyrrolidin-1-yl] derivative 4, and approximately two times more active than the racemate, 7-[(3RS)-hydroxypyrrolidine-1-yl] derivative 10.