The gangliosides GD3, GD2 and GM2 are expressed on the cell surface of malignant melanomas, GD3 being the most abundant. We have shown that immunization of melanoma patients with GM2 adherent to Bacillus Calmette‐Guerin (GM2/BCG) induced an IgM antibody response. Vaccines containing GM2‐keyhole limpet hemocyanin (KLH) conjugate and the immunological adjuvant QS‐21 induced a higher titer IgM response and consistent IgG antibodies. Patients with antibodies against GM2 survived longer than patients without antibody. On the other hand, our previous trials with GD3/BCG, GD3 derivatives including GD3‐lactone (GD3‐L)/BCG failed to induce antibodies against GD3. In our continuing efforts to induce antibody against GD3, we have immunized groups of 6 melanoma patients with GD3‐KLH or GD3‐L‐KLH conjugates containing 30 μg of ganglioside plus 100 μg of QS‐21 at 0, 1, 2, 3, 7 and 19 weeks. Prior to vaccination, no serological reactivity against GD3 or GD3‐L was detected. After immunization, IgM and IgG antibodies were detected against both GD3 and GD3‐L in the GD3‐L group exclusively. The GD3‐L‐KLH vaccine induced IgM titers against GD3‐L of 1:40–1/1,280 in all patients and IgG titers of 1/160–1/1,280 in 4 patients. These antibodies also strongly cross‐reacted with GD3. ELISA reactivity was confirmed by immune thin‐layer chromatography on GD3 and melanoma extracts. Sera obtained from 4 of these 6 patients showed cell surface reactivity by FACS and from 2 showed strong cell surface reactivity by immune adherence (IA) assay and complement lysis against the GD3 positive cell line SK‐Mel‐28. Int. J. Cancer 85:659–666, 2000. © 2000 Wiley‐Liss, Inc.