Résumé : The antimicrobial activity of cefpirome on a culture of Escherichia coli was measured by kinetic turbidometry and killing curves. At lower concentrations (0.06 μg/ml to 1 μg/ml), the killing rate was independent of drug concentration. At the higher concentrations (4 μg/ml to 256 μg/ml), the bactericidal activity depended on drug-concentration. The measurement of the early increase in optical density was predictive of the two thresholds of bactericidal activity.