The susceptibility of 677 clinical bacterial isolates to temocillin was determined by broth microdilution and disk diffusion methods for the purpose of evaluating disks with three different temocillin concentrations and determining the temocillin disk diffusion interpretive criteria. The 60 microgram temocillin disk provided the highest interpretive accuracy (96.2%), although the 30 microgram disk differed by having only three (1.2%) additional minor interpretive errors. Based on available temocillin pharmacokinetics and recommended dosage schedules, the minimum inhibitory concentration breakpoints chosen were: greater than or equal to 32 micrograms/ml = resistant and less than or equal to 16 micrograms/ml = susceptible. The corresponding disk diffusion zone diameter breakpoints for the 60 microgram disk were less than or equal to 17 mm and greater than or equal to 21 mm; zone diameters of 18-20 mm were considered intermediate. For the 30 microgram disk these were less than or equal to 15 mm, greater than or equal to 19 mm and 16-18 mm respectively.