Frequency effects in auditory backward masking were examined by psychophysically determining the thresholds of 0.5‐, 1‐, 3‐, 5‐, and 7‐kHz sinusoidal probes followed by a broadband noise masker. For each probe frequency, backward masking decreased approximately exponentially as the temporal interval between the probe and masker was increased. The rate of this exponential decay increased with increasing probe frequency. This latter result is consistent with Duifhuis’ [J. Acoust. Soc. Am.54, 1471–1488 (1973)] theory which attributes backward masking to the temporal overlap of cochlear responses to the probe and masker.