Levels of monaural signals at behavioral threshold were determined by a psychophysical method of adjustment for seven highly trained listeners. Thresholds were studied as a function of signal frequency (octave steps, from 0.125 to 8 kHz) and of signal duration (logarithmic steps, from 16 to 1024 msec). Measurements were made in the presence of a contralateral broad‐band masking noise with a spectrum level of 30 dB SPL. The time constant, τ estimated from at least 12 replications of each measurement, was found to range systematically from values considerednormal(125–175 msec) by some earlier investigators, at low frequencies, to much lower values (30–70 msec) at high frequencies. Comparison between the performance of listeners with normal audiograms and those with high‐frequency hearing loss shows this interaction between frequency and the time constant to be similar for both samples. The data are also compared to the results of a second experiment that employed a two‐alternative forced‐choice psychophysical method.