Frequency difference limens (DL) were measured for Gaussian noise having band widths of 12 to 64 cps centered at 800 cps and for a pure tone, also at 800 cps. Six listeners were used, and the DL's were defined as the probable errors of the fitted transition curves. For band widths wider than 8 cps, the DL rises regularly. Between 12 to 8 cps the threshold changes are small, having a minimum at about 8 cps. None of the DL's for noise approach that of the pure tone, all being at least twice as large. It is suggested that the failure of ΔF for narrow bands of noise to converge on ΔF for a pure tone is due to the dependence of frequency discrimination on intensity discrimination. In narrow bands of noise, the auditory system follows the amplitude fluctuations, which increases the uncertainty of judgments of intensitive differences. For the bands of noise wider than 8 cps, ΔF increases directly with band width. A linear increase in ΔF with band width is predicted for a limited range of band width and was found to fit the data.