Cultures and antibiotic sensitivities were determined for 84 patients in the oral surgery clinic who had diagnoses of odontogenic infections. Data tabulated from the results of the bacteriologic cultures and antibiotic sensitivities disclosed the five organisms most frequently involved. Antibiotic efficacy for each of the antibiotics used in sensitivity determinations was calculated on the basis of the percent sensitivity of a given organism to the given antibiotic, and the percent of patients with infections resulting from the given organism, both expressed as decimals. Antibiotics were then arranged in order of greatest to least efficacy on the basis of chloramphenicol as 100 percent. Efficacy values, sigma and lambda, were compared for the antibiotics. It was concluded that those antibiotics below penicillin on the efficacy table were less useful in the initial antibiotic treatment of odontogenic infections. Chloramphenicol was effective against every microorganism isolated during this investigation, but its use should be tempered with clinical judgment. Erythromycin should be given consideration as a replacement for penicillin as the preferred drug in the initial treatment of odontogenic infections on the basis of its high efficacy rating and freedom from potentially serious allergic or other untoward manifestations.