Blastocystis hominis, a protozoan parasite of the human gastrointestinal tract and an organism implicated in the causation of human diarrhea, is being studied in terms of its morphology, physiology and sensitivity to metronidazole, enterovioform and similar drugs. This sporozoan may contain hundreds of mitochondria, and their enzyme activity, if any, are subjects of the study. Mean generation time of B. hominis is from 5-10 hours. Individual generation time is 30 minutes to 90 minutes. B. hominis is sensitive to metronidazole, enterovioform, and other oxyquinoline derivatives. Drug testing is now being expanded to cover other appropriate candidate drugs. Cell division of B. hominis is commonly asexual, with sexual reproduction occurring rarely.