GM2 and GD2 have been intensely studied as tumor antigens of neuroectodermal-origin tumors. We have established several mouse or rat IgM anti-ganglioside GM2 and GD2 MoAbs and applied them in antigen-specific drug delivery. In the immunofluorescence assay, anti-GM2 MoAbs bound to neuroblastoma cells and leukemia cells, and anti-GD2 MoAb bound to neuroblastoma cells and melanoma cells. Sulfhydryl subunits of reduced IgM were directly coupled to maleimide groups on the surface of the liposomes followed by the incorporation of adriamycin by the use of Na+/K+ chemical gradient. The resultant immunoliposomes had a size of 86 nm-diameter containing approximately 400 molecules of adriamycin in its unilamellar structure and 17 molecules of the MoAb on its surface. Mouse anti-GM2 MoAb lost the binding specificity when covalently bound to the liposomes. The immunoliposome coupled with mouse anti-GD2 MoAb retained targeting activity to the antigen-positive neuroblastoma cells, IMR-32. However, it did not kill IMR-32 cells, probably because the amount of adriamycin taken up by the tumor cell was below the fatal amount. The immunoliposome coupled with rat anti-GM2 MoAbs delivered adriamycin to the neuroblastoma cells, IMR-32, and leukemia cells, TYH, in the antigen-specific manner. It also target-specifically suppressed the (3H)thymidine-uptake of the cells while the same concentration of adriamycin in the free form killed all the cell lines examined. IMR-32 cells had GM2 and GD2 in almost the same amounts, and interacted with either mouse anti-GD2 MoAb--immunoliposome or rat anti-GM2 MoAb-immunoliposome. The different cytotoxic activities of the two immunoliposomes against IMR-32 cells was probably due to the difference in the facility of internalization of the immunoliposomes after binding.