Summary 1. A modification of the zinc sulfate centrifugal flotation technique is described for concentrating cysts of E. coli and E. histolytica from stools and cultures in watch glasses with minimum amounts of foreign material. 2. Several strains of E. coli have been cultivated from cysts that were freed by microisolation from bacteria and transferred into riced whole egg medium that was seeded with organism t and B. subtilis. 3. Encystation of E. coli in vitro was obtained by the method of Dobell in cultures with an undetermined number of species of bacteria and also with only three species, organism t, B. subtilis and Streptococcus zymogenes. 4. On the basis of culturability and microscopic appearance the cysts of E. coli were not demonstrably affected by drying; cysts of E. histolytica were irreversibly damaged by drying.