Motor neurone disease, or amyotrophic lateral sclerosis, is a serious progressive neurological disorder, characterized by loss of UMN and LMN. Pathological features include characteristic intracytoplasmic MN inclusion bodies and appearances on ubiquitin staining. The aetiopathogenesis of the disease remains unknown and there is, to date, no effective treatment. Several abnormalities have been demonstrated in neurotransmitter, neuropeptide and gene expression studies. Abnormalities in glutamate metabolism have led to the excitotoxin hypothesis of MN destruction. Other theories include deficits in MN trophic factors, trans-synaptic degeneration, impaired ability to detoxify putative toxic agents and impaired DNA/RNA metabolism. The existence of familial forms, some of which show linkage to markers in chromosome 21, allows a genetic approach to the mechanisms of disease. Recent studies suggest that mutations in the Cu/Zn SOD gene may be important in some of the familial forms. The atypical forms seen in the Western Pacific have stimulated a search for environmental agents. Agents undergoing therapeutic trials at present include CNTF, IGF1 glutamate antagonists, branched-chain amino acids and TRH analogue.