Anaerobic fermentation of feedlot swine waste combined with corn was carried out in a newly designed laboratory silo. A lactic acid fermentation with rapid odor control resulted. Initial numbers of total and lactic acid bacteria (all per dry g) were 107. More than 75% of the initial total population were lactobacilli that increased 27-fold at 24 h and immediately entered a phase of decreasing viable numbers. The lactobacilli were largely the streptobacterium type. Lactobacilli were counted in both plates and roll tubes, and the counts in the roll tubes were as much as 100-fold greater; the difference was attributable to anaerobic lactobacilli. After 38 d, lactobacilli were no longer found in plates, but obligately anaerobic lactobacilli persisted at 103 through 90 d. Fecal coliform bacteria, initially present at 106, were not detected after 24 h. Yeast cells, starting at 106, decreased 100-fold at 3 d, and clostridia nerver exceeded 82 cells. Both groups were of minor importance in this fermentation. Virtually all the acid produced was lactic, measuring 3.83 (% dry matter) at 2 d and rising to a maximum of 12.45 at 69 d. In response, the starting pH of 6.80 decreased to 4.23 and then remained near 4 thereafter. Fumaric and succinic acid levels nerve exceeded 0.2 (% dry matter). Of the volatile fatty acids measured, acetic was maximum at 0.45 (% dry matter), but n-butyric and propionic were never more than 0.06. Fermenting a swine waste-corn mixture in a laboratory silo conferred preserved properties and diminished disease potential on a moist silage that can serve as a major component in an animal ration.