Ceftizoxime was tested in triplicate against 100 clinical strains of Neisseria gonorrhoeae in accordance with National Committee for Clinical Laboratory Standards guidelines to establish susceptibility testing interpretive criteria. The MICs for 50 and 90% of the strains tested were 0.008 and 0.03 microgram/ml, respectively. These results confirm those of other studies reporting ceftizoxime's excellent activity against gonococci. Because no resistant strains were identified, a breakpoint MIC of < or = 0.5 microgram/ml was selected, with a correlate zone diameter of > or = 32 mm. Ceftizoxime appears to represent an alternative to other beta-lactamase-stable beta-lactams for cost-effective therapy of uncomplicated gonorrhea.