SUMMARYThis study presents a comparative analysis of gangliosides from lymphoid (spleen and thymus) and other (brain, liver, lungs and muscle) tissues of C57BL/6 mice lacking the gene for b 2 -microglobulin (b 2 M), a constitutive component of the MHC class I molecule. Ganglioside fractions in the tissues of mice homozygous (b 2 M-/-) and heterozygous (b 2 M-/+) for the gene deletion were determined by high performance thin-layer chromatography (HPTLC), followed by immunostaining with specific polyclonal antibodies. Ubiquitous gangliosides G M3 (Neu5Ac) and G M3 (Neu5Gc) were the dominant gangliosides in the lungs of the control b 2 M-/+ mice, whereas the homozygous knockout mice had substantially decreased expression of these structures. The lungs of the b 2 M-/-mice also had reduced expression of T-lymphocyte-specific G M1b -type gangliosides (G M1b and GalNAc-G M1b ). b 2 M-deficient mice also had more G M1a and G D1a gangliosides in the liver, and several neolacto-series gangliosides were increased in the brain and lungs. This study provides in vivo evidence that the b 2 M molecule can influence the acquisition of a distinct ganglioside assembly in different mouse organs, implicating its non-immunological functions.