Twenty diabetic foot ulcers were cultured using optimal microbiologic techniques. Anaerobic bacteria coexisted with the more commonly recognized aerobic bacteria in 18 specimens. There were a total of 116 isolates with an average of 5.8 species per specimen (3.2 aerobes and 2.6 anaerobes). The principal isolates were Bacteroides species (sp.) (17 strains), peptococci (16), Proteus sp. (11), enterococci (9), Staphylococcus aureus (7), clostridia (7), and Escherichia coli (6). When antimicrobial therapy is indicated the selection of agents should consider the likelihood of a complex aerobic-anaerobic flora.