Temporal Modulation Transfer Functions (TMTF's) were obtained by measuring the threshold amplitude of sinusoidal modulation as a function of modulating frequency. For modulation frequencies below approximately 800 Hz, TMTF's obtained with a continuous wide-band noise carrier generally show the low-pass characteristic reported previously [J. Acoust. Soc. Am. 53, 314(A) (1973)], That is, with increasing modulation frequency the amplitude of modulation required for threshold remains constant up to approximately 10 Hz and then increases monotonically up to 800 Hz. The interpretation is that at high modulation frequencies the auditory system temporally “smooths” the amplitude fluctuations produced by modulation and the observer therefore requires greater modulation amplitude at the input in order to detect the modulation. For modulation frequencies greater than 800 Hz, modulation threshold is independent of modulation frequency and can be predicted from the increment threshold for wide-band noise. The form of the empirical TMTF generally agrees with that predicted by the familiar model consisting of half-wave rectification followed by “leaky integration.” The time constant of the integrator is estimated to be 3 msec. [Research supported by NIH.]