Purification was by electroelution from native polyacrylamide gels or by sequential use of three columns. Electroelution was faster and resulted in a higher yield (23.4 vs 1.6%) than column purification. The enzyme had a molecular mass of 187 kDa, and the isoelectric point ranged from 5.4 to 6.0. ALP purified by electroelution was used as the antigen to immunize rabbits for polyclonal antibody (PAb) production. Western blot analysis showed that PAbs cross-reacted with bovine milk and placenta ALP, but did not cross-react with ALP from calf or bovine intestinal mucosa, Escherichia coli or with other milk proteins.