The standard disk diffusion method of Bauer et al. (Am. J. Clin. Pathol. 45:493-496, 1966; National Committee for Clinical Laboratory Standards, Performance standards for antimicrobial disc susceptibility tests, approved standard ASM-2, 2nd ed., 1979) was used to monitor the potency of 16 Autobac antibiotic elution disks over an 8-month period. Results obtained by using the three recommended Autobac control strains showed excellent reproducibility. Zones sizes were all within a 5-mm range, and standard deviations ranged from 0.6 to 1.3 mm.