Monoclonal and/or polyclonal antibodies were generated against the products synthesized from two portions of the ret proto-oncogene (c-ret) cDNA expressed in Escherichia coli. These antibodies were reactive in immunoblotting with 150 kd and 170 kd proteins in cell lysates from three human neuroblastoma cell lines expressing the ret proto-oncogene. When the neuroblastoma cells were treated with tunicamycin, a protein with an apparent molecular weight of 120 kd, which is consistent with that of the c-ret protein predicted from the cDNA sequence, appeared on immunoblots. These results indicated that the 150 kd and 170 kd proteins in neuroblastoma cells are produced from a single polypeptide of 120 kd by posttranslational glycosylation. Furthermore, the antibodies detected a unique 190 kd protein as well as 150 kd protein in a cell lysate from THP-1 human monocytic leukemia cell line, suggesting that glycosylated forms of the c-ret protein are different between neuroblastoma and leukemia cells.