Résumé : M.K. 0366, a new quinoline compound with a very broad spectrum of antibacterial activity remains active on multiresistant strains. The minimum inhibitory concentrations (MIC) were determined by an agar-dilution method. MIC of M.K. 0366 required for inhibition of 90% of clinical strains was: Staphylococcus aureus 0.8 μg/ml; Pseudomonas aeruginosa 1.56 μg/ml; Enterobacter cloacae 0.08 μg/ml and Serratia marcescens 3.12 μg/ml. We confirm the very low minimum inhibitory concentrations against Haemophilus influenzae (β-lactamase positive and negative): 0.08 μg/ml. M.K. 0366 appears to be a very promising drug against multiresistant bacteria frequently involved in nosocomial infections.