THE presence of iso-butyric acid in silage has not been reported since Kline1, using a qualitative chemical method of detection, claimed to have found it in the material in the surface layers of a silo. Barnett2 during comprehensive investigations into the formation of the volatile fatty acids in silage found no trace of it, but the results of Lessard, Briggs and Scaletti3 suggest its presence in samples of alfalfa silage made in the laboratory. No quantitative determinations of the acid have been reported.