A report on a patient who developed profuse fasciculations following diphenylhydantoin therapy for 30 months with subsequent complete recovery on cessation of therapy is presented. In view of the considerable variability of spontaneous potentials generated in spinal motor neurones, in vitro studies and pathological states with respect to shape, amplitude, frequency and duration, caution is advised in the assessment of the clinical significance of fasciculations. The possibility that our patient represents an instance of a ‘reversible form of motor neuron disease’ is entertai