A study was designed to compare the systemic absorption of metronidazole by the oral and vaginal routes. Nine subjects received single 500-mg doses of the oral, vaginal insert, and vaginal cream preparations on three occasions. Approximately 20% bioavailability was demonstrated from both vaginal forms. Mean peak plasma concentrations were 15.56 micrograms/mL for the oral form, 1.86 micrograms/mL for the cream, and 1.89 micrograms/mL for the insert. The mean times to peak concentration were 1.23 hours for the oral dose and 11.11 hours and 20.11 hours for the cream and insert, respectively. The data demonstrate that some vaginal absorption occurs from both the cream and insert preparations of metronidazole.