Cefditoren (ME 1206) is a new cephalosporin available for oral administration as the pivaloyloxymethyl ester (ME 1207). The effect of medium formulation. pH, cation concentration and inoculum on the in vitro activity of cefditoren was investigated prior to determining its comparative antibacterial potency against a wide range of clinical bacterial isolates, its bactericidal activity against susceptible strains and the duration of its post-antibiotic effect (PAE). Cefditoren was shown to possess a broad-spectrum of cidal antibacterial activity against both Gram-positive and Gram-negative species with stability to many beta-lactamases of clinical importance. Its activity against Gram-positive species was similar to augmentin and cefuroxime, but superior to that of cefaclor and cefixime, while its beta-lactamase stability was similar to that of cefixime and ceftazidine, characterizing it as a third generation cephalosporin. Investigation of the effect of laboratory variables on the in vitro activity of cefditoren indicates that it will present no special problems when tested in the clinical setting against bacterial pathogens. PAE of 0.9 h, or greater, for Staphylococcus spp, Streptococcus pneumoniae and Moraxella catarrhalis may support the use of an extended dose-interval when cefditoren is used for the treatment of respiratory tract infections.