Eight subjects trained in listening were given a variety of taped programs of frequency glissando consisting of items which began at 1500 cps and proceeded at 50 phons either up or down in frequency. S's were required to judge “higher” or “lower.” Periods of glissando from 0.2 to 10 sec and rates of change from 0.5 to 100 cps/sec were used. Sensitivity to this type of frequency modulation is surprisingly good, and inter‐subject variation is not excessive; thus it could well form one sensory input to certain man‐machine systems, either on an absolute or a relative basis. OneS, extremely poor on the more usual pitch test by the constants method, was not much worse than average on glissando. For mostS's, a constant emerges at a total of about 5‐cps change, such that sensitivity to 0.5 cps/sec change over 10 sec is about equally as difficult as 5 cps/sec change over 1 sec, and so on. This constant is in fact of the same order of magnitude as the traditional DL for pitch.