Responses to glissando at 1500 cps at a 50-phon level using trained and untrained listeners are analyzed. The sensitivity to this type of frequency modulation is surprisingly good. A constant of 5 cps change emerges indicating that sensitivity depends on a linear relationship between rate of change and stimulus duration. This constant is of the same order of magnitude as the traditional DL for pitch memory. The low observed relationship of glissando to either pitch discrimination by the constants method or with sensitivity to the presence or absence of sinusoidal frequency modulation indicates that probably a third distinct pitch factor is represented.