Employing RMG-1 cells derived from human ovarian adenocarcinoma and COS-1 cells transfected with cDNA for beta 1,4-galactosyltransferase, we first investigated the intracellular localization of this enzyme anal secondly assayed separately the two types of soluble forms of it (designated as normal GalT and GAT) in their culture supernatants. As results, the binding of anti-beta 1,4-galactosyltransferase monoclonal antibody was strongly positive at the Golgi area surrounding nuclei and the staining pattern was the same between RMG-1 cells and COS-1 transformants. These data demonstrated that the cells were producing beta 1,4-galactosyltransferase and had the ability to release it into the culture medium. As for the two soluble farms released from the cells, they were simultaneously detected in the culture medium by Western blotting and enzyme immunoassay using monoclonal antibodies, i.e., Mab8628 reactive to both GAT and normal-GalT and Mab8513 specific for GAT, indicating that both were derived from RMG-1 and from the cDNA introduced into COS-1 cells. Since serum-GAT clinically reflects tumor growth more accurately or specifically than normal GalT does, RMG-1 and COS-1 cells having cDNA for beta 1,4-galactosyltransferase would be promising as sources of these enzymes in order to investigate the differences in the behaviors of normal GalT and GAT associated with ovarian malignant tumors.