This study evaluated the in vitro activity of A-86719.1, a novel 2-pyridone antimicrobial agent. The drug inhibited all tested members of the family Enterobacteriaceae at less than or equal to 0.5 mu g/ml and all tested Pseudomonas aeruginosa, Burkholderia (Pseudomonas) cepacia, and Xanthomonas maltophilia strains at less than or equal to 2 mu g/ml. All but two strains of gram-positive bacteria were inhibited by less than or equal to 1 mu g of the new drug per ml, including isolates highly resistant to ciprofloxacin.