The use of antimicrobial prophylaxis in the presence of posterior nasal packing for the treatment of posterior epistaxis remains controversial. Twenty patients were prospectively randomized into this placebo-controlled, double-masked pilot study to receive either placebo or cefazolin sodium. Antibiotic-impregnated posterior gauze packing was employed in all patients. No infectious complications were noted in either group. The packings from the patients in the placebo group were foul smelling and heavily colonized with gram-negative bacteria while the packings from the antibiotic group were odor-free and lightly colonized with gram-positive organisms. This preliminary study suggests the usefulness of antimicrobial prophylaxis for preventing complications from posterior nasal packing, although a larger sample size will be needed to decrease the type II (beta) error.