The expression and properties of alkaline phosphatase (ALP) in Ecal09 cells, a cell line derived from human esophageal cancer were studied with specific inhibition assay and polyacrylamide gel electrophoresis. The results showed that ALP of Ecal09 cells was heat stable and was strongly inhibited by L-phenylalanine, but slightly inhibited by urea. Prednisolone could causedramatic increase in activity of ALP, but no change in ALP isozyme and concomitant increase in lactic dehydrogenase activity were found after prednlsolnne treatment. The results suggested that placental alkaline phosphatase as an oncodevelopmental gene product could be expressed ectopically by Ecal09 cells and prednisolone could specifw.ally induce increase in its activity.