The situation regarding the treatment of human Giardia and Trichomonas infections and the intestinal and tissue stages of Entamoeba histolytica with metronidazole and other 5-nitroimidazoles is currently satisfactory (Table 1; Mehlhorn 2000). Following correct and rapid diagnosis, the parasites are eliminated reliably and completely. The situation in cases of infection with Acanthamoeba (often involving the eyes) or with Naegleria (often involving the brain) is serious, however. In both cases, there is no drug of choice available. Treatment consists of relieving the symptoms and/or preventing local degeneration.