The rectal absorption of metronidazole from an aqueous suspension, a fatty suppository and three different polyethylene glycol suppositories was studied in healthy volunteers and compared with absorption from an oral solution. Rectal absorption was found to be rather slow for all suppositories. Of all rectal dosage forms, the polyethylene glycol suppositories gave the highest peak plasma levels and the highest relative bioavailability. Compared with oral administration, a relative bioavailability of 80% could be obtained.