The frequencies of bacterial isolation and susceptibilities to antimicrobial agents were investigated on 538 bacterial strains isolated from patients with urinary tract infections (UTIs) in 9 hospitals during the period of June 1998 to May 1999. Of the above bacterial isolates, Gram-positive bacteria accounted for 30.3% and Gram-negative bacteria accounted for 69.7%. Susceptibilities of several isolated bacteria to antimicrobial agents were as follows; against Enterococcus faecalis isolated from patients with UTIs, vancomycin (VCM), ampicillin (ABPC) and imipenem (IPM) had strong activities. Among E. faecalis strains, those with low susceptibilities to all drugs have increased in 1998, compared with those in 1997. VCM showed the highest activity against MRSA isolated from patients with UTIs. The MICs of VCM for all 34 strains were equal to or lower than 2 micrograms/ml. Arbekacin (ABK) was also active against MRSA with the MIC90s of 2 micrograms/ml. Against Escherichia coli and Klebsiella pneumoniae, all drugs except penicillins were active. Particularly, meropenem (MEPM) showed the highest activity with the MICs of 0.125 micrograms/ml or below. Almost all the drugs except minocycline (MINO) showed high activities against Proteus mirabilis. Against Pseudomonas aeruginosa, all drugs were not so active, with the MIC90s of 16 micrograms/ml or above. MEPM, IPM and gentamicin (GM) showed high activities against Serratia marcescens. Generally, it seemed that resistant strains of S. marcescens had decreased since 1996.