This paper elucidates the status of the different morphological forms
of Blastacystis and reports the existence of thin- and thick-walled cy
sts in B. hominis on the basis of current experimental evidence. It is
suggested that the thin-walled cysts are autoinfectious, leading to m
ultiplication of the organism in the intestinal tract. The thick-walle
d cysts are responsible for external transmission via the faecal-oral
route. A life cycle for B. hominis is postulated on the basis of these
findings.