Agar dilution and disc diffusion susceptibility testing of erythromycin were performed for contemporary isolates of Bordetella pertussis with the use of charcoal media. Minimum inhibitory concentration (MIC) values ranged from < or = 0.016-0.5 mg/l and the MIC(50) and MIC(95) were 0.125 and 0.25 mg/l respectively. Disc diffusion zone sizes were interpretable after either 48 or 72 h of incubation and all inhibition diameters were > or = 37 mm.