Treatment. The initial choice of drug was Metronidazole (MZ) in all cases. Metronidazole was used in three dosages: 2 g once daily for 3 days, 500 mg three times daily for 10 days, or 750 mg three times daily for 10 days. Initially, patients were given 2 g once daily, but as we saw a very limited effect at this dosage, subsequent patients were initially given 500 mg three times daily. If this had no clinical and no microbiological effect, 750 mg three times daily was given, and if still no effect, patients were treated with Tetracycline (TE) 500 mg four times daily for 10 days. In one case, a patient resistant to all treat- ments was given a trial of Mebendazole (100 mg three times separated by 2 weeks) before a trial of MZ to eliminate Enterobius vermicularis if present, as this has been proposed as a vector for D. fragilis.26