Blastocystis hominis cysts in faeces can be concentrated on Ficoll col
umn. They are pleomorphic in shape having a mean diameter of 6.65 mu m
(S.D.=2.32), They may or may not have a membranous layer surrounding
them. The membranous layer tends to come off with pressure or dying of
the specimen and corresponds to the fibrillar layer observed under th
e electron microscope. The Ficoll concentration technique is also usef
ul for concentrating other protozoan cysts.