Ro 09-1227 is a novel 7-position catechol-substituted parenteral cephalosporin that also has a 3-position radical similar to previously described cephems. The Ro 09-1227 spectrum was slightly wider than that of ceftazidime against members of the family Enterobacteriaceae tested, principally because of greater activity against species producing Richmond-Sykes type I beta-lactamases. Ro 09-1227 was also more active than ceftazidime against some strains producing extended-spectrum plasmid-encoded beta-lactamases, such as TEM-3, -4, -5, -6, -7, and -9, SHV-2 and -3, and CAZ-2. Most strains of Pseudomonas aeruginosa, Xanthomonas maltophilia, and Acinetobacter spp. were also more susceptible to Ro 09-1227 than cefotaxime, ceftriaxone, cefoperazone, and ceftazidime. Haemophilus influenzae (MIC for 90% of strains tested [MIC90], 0.5 micrograms/ml), Neisseria gonorrhoeae (MIC90, 0.015 micrograms/ml), and Moraxella (Branhamella) catarrhalis (MIC90, 0.5 micrograms/ml) were also Ro 09-1227 susceptible. Ro 09-1227 activity against important gram-positive cocci was most comparable to that of ceftazidime. Bacteroides fragilis (MIC90, greater than 32 micrograms/ml) and the enterococci (MIC90, greater than 32 micrograms/ml) were resistant to Ro 09-1227. These in vitro results indicate that this catechol-substituted cephalosporin may be useful as an empiric agent, especially for some isolates resistant to currently available broad-spectrum cephalosporins.