Electrodiagnosis plays an important role in the early detection and characterization of inflammatory demyelinating polyradiculoneuropathies, because timely treatment reduces morbidity and disability. The challenge consists of defining electrodiagnostic criteria that are highly specific for primary demyelination but sufficiently sensitive to be useful in clinical practice. We compared 10 published sets of criteria in 53 patients with demyelinating Guillain-Barré syndrome (GBS) and 28 with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). Specificity of criteria sets was tested in 40 patients with amyotrophic lateral sclerosis (ALS) and 32 with diabetic polyneuropathy (DPN). Sensitivity ranged from 24 to 83% (mean, 54.3%) in GBS and 39 to 89% (mean, 64.9%) in CIDP. With regard to ALS, specificity was 100% for nine sets but was 97% in one. In contrast, 3-66% of DPN patients fulfilled criteria in eight of ten sets. We propose a set of criteria with 72% and 75% sensitivity in our GBS and CIDP patient series, respectively, and 100% specificity with regard to ALS and DPN. Our data illustrate that most, but not all, patients can be electrodiagnostically ascertained.