Frequency difference limens were determined as a function of stimulus duration in five normal‐hearing and seven hearing‐impaired subjects. The frequency DL duration functions obtained from normal‐hearing subjects were similar to those reported by Liang and Chistovich [Sov. Phys. Acoust.6, 75–80 (1961)]. As duration increased, the DL’s improved rapidly over a range of short durations, improved more gradually over a middle range of durations, and reached an asymptote around 200 ms. The functions obtained from the hearing‐impaired subjects were similar to those from normal subjects over the middle and longer durations, but did not display the rapid changes at short durations. The paper examines the ability of a variation of Zwicker’s excitation‐pattern model of frequency discrimination to explain these duration effects. Most, although not all, of the effects can be adequately explained by the model.