The susceptibilities of 347 urine isolates of enterococci (Streptococcus faecalis, 44%; S. faecalis subsp. zymogenes, 37%; S. faecalis subsp. liquefaciens, 19%) to ampicillin, azlocillin, mezlocillin, piperacillin, vancomycin, gentamicin, erythromycin, rosaramicin, rifampin, rifampin plus trimethoprim (1:4), trimethoprim-sulfamethoxazole (1:20), and chloramphenicol were determined by the agar dilution technique. There were no significant differences in susceptibility to individual agents among the subspecies of S. faecalis. Azlocillin and mezlocillin (MIC for 90% of isolates, 0.78 micrograms/ml) and piperacillin, ampicillin, and vancomycin (MIC for 90% of isolates, 1.56 micrograms/ml) were the most active agents and were significantly more potent than the other reference antibiotics tested.