Clinical data were collected prospectively from a series of 160 patients presenting with mammalian bite wounds. Anaerobic and aerobic cultures were prepared from sterile swabs placed in 65 bite wounds prior to cleansing. Infection was noted in 11 of 22 cat bites, six of 37 human bites, three of 80 dog bites, and in none of the 21 bites caused by other mammals. Pasteurella multocida was recovered from six infected cat and dog bites, all of which developed infection within 24 hours of injury. Staphylococcus aureus and Streptococcus viridans were the principal pathogens isolated from the remaining infected cat, dog, and human bites. Infection most commonly followed puncture wounds caused by cats (10/19) and lacerations into subcutaneous tissue of the hand caused by humans (4/17). None of the 10 sutured wounds became infected. All infected bite wounds responded to antibiotic therapy. No conclusions regarding the value of prophylactic antibiotics could be made.