Some reports have called sensory ataxic neuropathy (SAN) associated with IgM antibody against b-series gangliosides a chronic form of Miller Fisher syndrome (MFS), but this has yet to be established. We examined five patients with SAN and eight patients with IgG anti-GQ1b-positive MFS. Only one patient with SAN complained of diplopia, whose ocular movement was not limited. The other four patients had neither diplopia nor limitation of ocular movement. All the SAN patients had severe deep sense impairment, whereas one patient with MFS showed only mild vibratory sense impairment. All sera from the SAN patients had remarkably high IgM antibody titers to the b-series gangliosides GD3, GD2, GD1b, GT1b, GQ1b, GQ1b alpha, fucosyl-GD1b, and alpha galactosyl [alpha fucosyl] GD1b. An absorption study confirmed that the anti-GQ1b antibodies cross-reacted with GD3, GD2, GD1b, and GT1b. In contrast, only two samples from the MFS patients had IgG antibody to GD3, and no sample reacted with GD2, GD1b, or GT1b. SAN has different clinical or serological features from MFS, and therefore is not a chronic form of it.