Preliminary studies were made on the numbers and characteristics of the micro-organisms on forage crops used for silage and on a number of plant species commonly included in forage used for ensiling at Beltsville. The predominating type of bacteria found on fresh forages was aerobic, chromogenic, non-spore-forming, rod types. Coli-form types, mainly of the genus Aerobacter, were also present in large numbers. Colonies of bacteria taken from forages harvested in spring were yellow and very uniform in type; colonies produced by bacteria from forages harvested late in the season were much more variable in type. It was considered that the predominating types of chromogenic bacteria found were an indigenous plant microflora. Endeavours to isolate Lactobacillus plantarum from fresh forages were largely unsuccessful. There was a tendency for populations of micro-organisms on the forages to increase as the plants matured. Populations also increased during the period between cutting and ensiling. Wilting for several hours in the field caused 7- to 17-fold increases in micro-organism numbers; these increases could not be accounted for by concentration attendant on a reduction of some 25% in the moisture content of the forages during wilting.