The effect of a single preoperative dose of metronidazole in the prevention of alveolitis sicca dolorosa (ASD) after surgical removal of one impacted, non-infected mandibular third molar was investigated. A patient sample of 270 were given either 1000 mg of metronidazole or placebo at least 30 min before surgery. The preoperative recordings included gender, age, tooth to be removed, experience of surgeon, time of test medication, and duration of surgery. No difference was found between the metronidazole and placebo groups in the occurrence of ASD. The duration of surgery and the experience of the operating surgeons had no effect on the occurrence of ASD. The present study failed to demonstrate any preventive effect of a single dose of metronidazole on the development of ASD.