The discrimination of a change in the intensity of a component or components of a multitone complex is reported as a function of a number of experimental variables [in humans]. In 1 experiment, changes in the shape of the spectrum were explored to determine which kinds of changes are more easily detected. Although different signal spectra produced different thresholds, the change in a single component produced the lowest threshold on an energy basis. Various binaural conditions were tested to determine if the shape or profile of the stimulus could be supplied by the ear opposite the one in which the signal was presented. Conditions where spectral contrasts were available to both ears simultaneously (diotic conditions) were much more sensitive than conditions where the spectral contrasts occurred for opposite ears (dichotic conditions). The level of the component at the signal frequency was varied relative to the other, equal amplitude, components to form a pedestal upon which the signal was added. Detection of the signal was roughly the same for pedestal levels within about .+-. 12 dB of the background except for conditions where masking was apparent.