Alkalinephosphatase, which is present in curds made from raw milk as well as from boiled milk, does not serve to differentiate them. It was found that incubation time or acidity (lactic acid equivalent of curd acidity incubated aseptically with heated milk) does not revive heat-denatured phosphatase. The reappearance was found to be due to phosphatase of microbial origin; it was not a case of reactivation of the denatured enzyme. Low intensity, but increasing slowly, of the activity of regenerated phosphatase in curd (permeability of the microbial cells to the testing reagents is probably limiting in the rate of reaction), presence of the enzyme in the sonicated cells of curd-forming microflora and absence of activity in the supernatant of the growth medium suggest that the formed enzyme is an intracellular one.