SUMMARY: Clone cultures of two strains of the rumen organism Eadie's Oval were established in vitro. Both strains were maintained anaerobically at 38 to 40° in liquid culture in the presence of bacteria, rumen fluid, a reducing agent and a CO2 gas phase. There was no growth in sterile or solid media. Growth and storage of glycogen occurred when each strain was incubated with one of a small range of simple carbohydrates; amino acids, fatty acids, proteins and polysaccharides did not support growth or glycogen synthesis. Neither strain survived freezing, but cultures were viable after two weeks at 4°; incubation at 44° resulted in no growth or the death of cultures.