1) The extracts obtained from homogenized tissues were centrifuged at 65,000xg and filtered through an Ultrogel AcA 34 column. Among the three major peaks obtained by gel filtration, the second peak fractions were further separated by isoelectric focusing. Isoenzymes of alkaline phosphatase were found only in the second peak.

2) Isoenzymes of alkaline phosphatase were distinguishable with pH 3.5-10 ampholytes. When pH 3-6 ampholytes were used, isoenzymes were more clearly separated, e.g., 4in serum, 5 in intestine and 2 each in the liver, pancreas, and bone.

3) Comparing the bands of the isoenzymes of alkaline phosphatase to those of serum, only the band with 5.04 pI was the same between serum and intestine.

These results indicate that several forms of alkaline phosphatase, even though all are from the rat, may exist; and some of the isoenzymes of alkaline phosphatase found in the serum originated from the intestine.