Summary While recording from a nasal plethysmograph, cervical sympathetic fibers to the nose were stimulated with a square wave current of varying frequencies. The other current characteristics were kept constant. Our results indicate that increasing the frequency of stimulation from 4/min to 10/sec caused a change in nasal vasoconstrictor response of approximately the full range from minimal to maximal. A frequency of only 2/sec caused a moderately strong vasocon-striction, when many cervical sympathetic nerve fibers were stimulated simultaneously.