Horizontal saccadic eye movement velocities have been measured in patients with multiple sclerosis and myasthenia gravis using a computerised electrooculographic technique. The ability to detect subclinical abnormalities of eye movement with this technique indicates that it is of diagnostic value in patients with suspected multiple sclerosis who present with only a single symptomatic lesion in the central nervous system. The technique is also of value in the diagnosis of myasthenia gravis as it provides a means of quantifying the response of the extra-ocular muscles to anticholinesterase preparations.