The agar dilution method was used to determine the inhibitory activity of cefotaxime (CTX) alone, desacetylcefotaxime (dCTX) alone, CTX plus dCTX, and cefoxitin against 74 clinical isolates of the Bacteroides species recovered from diabetic patients with foot ulcers. The study concluded that the addition of dCTX to CTX increased the inhibitory activity from 45% to 73% for all strains tested and from 50% to 81% among the 32 strains of Bacteroides fragilis. This synergistic interaction against B. fragilis resulted in a four- to nine-fold reduction in the MIC of seven strains (64-128 micrograms/ml, resistant category MICs). While the lowest CTX MIC for B. fragilis was 2 micrograms/ml (four strains), the addition of dCTX also produced a remarkable reduction in susceptible range CTX MICs to 0.05-2 micrograms/ml in 16 strains (50%). The overall susceptibility to cefoxitin and CTX plus dCTX was as follows: 100% and 100% for Bacteroides vulgatus, 50% and 66% for Bacteroides thetaiotaomicron, 100% and 33% for Bacteroides ovatus, and 83% and 82% for Bacteroides species other than the B. fragilis group.