THE PALMOMENTAL reflex, first described 30 years ago by Marinesco and Radovici,1is a fleeting unilateral contraction of the chin muscle on stimulation of the thenar eminence of the ipsilateral hand. It has received only cursory attention except in the Continental literature. Its reported incidence in the normal adult population has ranged from zero to 58 per cent; most observers have found it with greater frequency in infants. Its pathway has not been defined, and no agreement has been reached concerning its clinical significance. For these reasons, a new study of this curious reflex was projected, aimed at (1) an analysis of its mechanism, variability and modifying factors and (2) a reappraisal of its clinical value. HISTORICAL REVIEW The reflex was discovered by Marinesco and Radovici in a patient with amyotrophic lateral sclerosis with extensive involvement of the corticobulbar tracts.2These investigators found the reflex in almost 50