When a mixture of sugarcane tops, alfalfa (20%) and milled malt (0.5%) was ensiled, a pronounced decrease of pH was observed during the first week corresponding to a rapid production of laotic and acetic acids. After that pH and acid production detached. The number of microorganisms increased during the first days of silage. Then aerobes rapidly decreased and were the fewer after 50 days of silage. Anaerobes also decreased but not so substantially. Lactic aoid producers rose very quickly during the first 4–5 days to became more or less constant after that. Filamentous fungi were predominant at the beginning among the fungal population, but later on almost disappeared and yeasts were found instead. During the silage process the amount of total reducing hydrolyzate increased and readily utilizable sugars were found after the microbial activity had ceased.