Protocol describes the growth and concentration of the alga Chlorogonium elongatum as a food source for culturing freshwater hypotrichs. Most freshwater hypotrichs (including Oxytricha nova, O. fallax, and O. trifallax; Euplotes aediculatus and E. eurystomous; and Stylonychia lemnae) can be grown to high density with Chlorogonium as the food organism. A similar regimen can be used to prepare other food sources such as Tetrahymena or bacteria (e.g., Aerobacter aerogenes).