The clinical efficacy of procaine penicillin and sulbactam-ampicillin was compared in patients with peritonsillar abscesses after peroral abscess drainage. Forty-two patients were randomly assigned to receive either procaine penicillin or sulbactam-ampicillin intramuscularly on an outpatient basis. The mean time required for clinical symptoms (throat pain, dysphagia and fever) to resolve was compared. No statistically significant difference was found between the clinical recoveries of patients using either antibiotic (P > 0.05). The authors conclude that intramuscular procaine penicillin can be safely prescribed on an outpatient basis to most patients with peritonsillar abscess after incision and drainage. In contrast, a broader spectrum and more expensive antibiotic, such as sulbactam-ampicillin, should be reserved for non-responders.