The positive significant correlation (r = 0.788, n = 37) was shown between the protease activity and the number of epithelial cells (not of leukocytes) in saliva. There was little protease activity observed in glandular saliva. It is possible to conclude from the results that a main source of salivary protease is the epithelial cells in saliva. It was also found that the oral prophylaxis reduced the numbers of epithelial cells and leukocytes and the protease activity.