In earlier studies using polyurethane foam for protozoan colonization, communities were established in 14 days (sampling weekly). Daily sampling in this study revealed that the number of colonizers increases with time and that flagellates make up the major portion of the early pioneer community becoming established in two to three days and reaching equilibrium much earlier that other taxonomic groups. Additional data indicate the flagellate component having reached equilibrium remains relatively stable during seasonal changes for as long as two years. A list of most common summer pioneer and persistant flagellates in two kinds of ecosystems is given.