Raw milk was flushed with 100 ml N2 min -1 during storage at 4°C. Microflora (total psychrotrophs, proteolytic psychrotrophs, lactic acid bacteria) in nitrogen-flushed milk exhibited a longer lag phase and slower growth rates than those in milk stored aerobically at 4°C. Although proteolytic psychrotrophs grew in nitrogen-flushed milk, proteinases could not be detected in these milk samples. Proteinase assays and electrophoresis showed extensive proteolytic activity and hydrolysis of β-casein in control milk but no detectable casein degradation in nitrogen-flushed milk, even after storage for 18 days at 4°C. This study shows the potential of controlled atmosphere storage of raw milk for inhibition of the accumulation of proteolytic enzymes from psychrotrophic bacteria.