A new metronidazole derivative, Tiberal (Ro-07-0207, Roche Laboratories), was evaluated in 22 children with Giardia lamblia infection. Seven patients received an oral dose of 1 g twice daily for one day; the remaining 15 patients received a single dose of 50 mg/kg. Parasitological cure was noted in all 22 patients. Significant side effects were observed only in those children who received the drug at the higher dosage regime. The present study also confirms the findings of other authors that a mucosal imprint method is more reliable than examination of stools, duodenal juice or jejunal biopsy material for the detection of G. lamblia infection.