Amotrophic lateral sclerosis diagnosis is based on clinical and electrophysiological findings. Transcranial magnetic stimulation and MRI can show abnormalities which are not specific, but which can confirm upper motor neuron involvement. The other tests are performed to exclude differential diagnosis. Tests which should be performed in every cases are: medullar MRI, blood counts, erythrocyte sedimentation, serum protein electrophoresis, calcium, phosphore, serological tests for HIV, siphylis, Lyme disease. Other tests are made in some clinical circonstances to exclude genetical disease or metabolic disorders (SMN gene, Kennedy gene, Hexosaminidase A, very long chaine fatty acids), haematological or paraneoplasic disorders (anti-neurons antibodies, PSA, CT of chest and abdomen, mammography, bone marrow biopsy) or inclusion myositis (muscle biopsy).