A method of producing monoclonal antibodies that bind to tumor-associated gangliosides, the method comprising: (1) immunizing a host with tumor cells; (2) boosting the host with a suspension comprising a mixture of tumor cell membrane and at least one purified lactonized tumor-associated ganglioside; (3) boosting the host with an immunogen comprising a lactone of a tumor associated ganglioside adsorbed on or incorporated into a carrier; (4) fusing immunized cells from the host with myeloma cells to form hybridoma cells: (5) selecting hybridoma cells that produce antibody that binds to the ganglioside of step (3); (6) culturing the selected hybridoma cells; and (7) recovering the antibody. Hybridomas and monoclonal antibodies produced by the above-described method. A passive immunization method for treatment of tumors containing gangliosides comprising administering to a subject: (A) a pharmaceutically effective amount of an antibody produced by the above described method. A method for detecting tumors containing gangliosides comprising: (A) contacting a test sample with an antibody produced by the above described method; and (B) assaying for the specific binding of the antibody to antigen in the test sample.