An increased frequency of serum IgM antibodies to beta-tubulin has been found by ELISA in patients with chronic inflammatory demyelinating polyneuropathy (CIDP) and the Guillain-Barré syndrome (GBS). We used an immunoblot technique to compare the frequency, titer and specificity of anti-tubulin IgM antibodies in 207 patients with different neuropathies, 109 with other neurological disease (OND) and 110 non-neurological controls. High titers of serum anti-tubulin IgM antibodies (> 1:1600) were present in 2 patients with CIDP (10.5%), 1 with multifocal motor neuropathy (MMN) (11%), 1 with GBS (1.8%), two with IgM monoclonal gammopathy, one with (1.3%) and one without neuropathy (2.1%), and in two with OND (1.8%). Even if the relative binding to alpha- and beta-tubulin differed among positive patients, in all IgM bound to both tubulin subunits. All positive patients had a similarly intense IgM reactivity with tubulin by ELISA that showed high anti-tubulin IgM in 4 additional CIDP patients (total positive by ELISA 30%) and in 7 of 23 normal subjects (30%). Even if high anti-tubulin IgM were slightly more frequent by immunoblot in chronic dysimmune neuropathies than in other diseases, possibly reflecting a secondary response to neural damage during an ongoing immune response, their relatively low frequency in these diseases does not seem to justify their measurement for diagnostic application.