In vitro antituberculous activities of three newly developed quinolones, fleroxacin (FLRX, AM-833), lomefloxacin (LFLX) and sparfloxacin (SPFX, AT-4140) were evaluated in comparison to that of ofloxacin (OFLX) using M. tuberculosis strains isolated from patients and the Ogawa egg medium. SPFX was apparently more active than OFLX, but both FLRX and LFLX were less active. SPFX inhibited completely the growth of all 20 strains of M. tuberculosis isolated from patients who were not previously treated with OFLX in a concentration of 1.25 micrograms/ml. However, this agent inhibited the growth of only 4 strains (28.6%) of 14 OFLX-resistant M. tuberculosis in a concentration of 1.25 micrograms/ml, suggesting a partial cross-resistance between SPFX and OFLX.