Résumé : The rate of bactericidal activity of a new cephalosporin, LY-163892, was compared with that of the combination of amoxicillin and clavulanic acid (in the proportion of 2 to 1) on ten strains of Haemophilus influenza beta-lactamase producers. The antibacterial activity of LY-163892 was bacteriostatic at 2 μg/ml during the first six hours, followed by a regrowth after 24 hours. When the concentration was increased from 8 to 128 μg/ml, the killing rate also increased. The bactericidal rate of amoxicillin/clavulanic acid was observed at 0.5 μg/ml but did not increase as the concentration was increased. The blood levels of LY-163892 in human volunteers for oral doses of 250 mg and 300 mg were 10.3 and 15.9 μg/ml, respectively. In conclusion, LY-163892 was bactericidal for H influenzae cultures at concentrations achievable in the blood of human volunteers.