Artificial polyurethane foam habitats were placed at weekly intervals in the epilimnion of Douglas Lake, Michigan from 11 July 1970 to 8 August 1970. At the time of the first examination on 14 August 1970 these had been immersed 32, 25, 18, 11 and 4 days respectively. A second examination was made on 27 September 1970. On each examination the number of protozoans that had colonized each polyurethane unit was determined. The results of this study indicate that while the number of species may be dependent upon the length of time of immersion for a certain period after placement, the number of species eventually becomes quite similar on each unit. This indicates that fresh-water protozoan communities fit the MacArthur-Wilson equilibrium model.