Abstract
Purified oocysts of Cryptosporidium were applied to the top of a sand filter which had been constructed in the laboratory. The filter was eluted with distilled water; fractions were collected and examined for Cryptosporidium by modified Ziehl-Neelsen technique and immunofluorescence microscopy and by an enzyme immunoassay. The results indicate that oocysts of Cryptosporidium do not easily pass through the sand filter, and that some disintegration of oocysts may occur during filtration.