Measurements have been made of the absorption of sound in air as a function of humidity in the frequency range from 2500 to 8000 Hz at pressures in the range from 0.2 to 0.9 atm, at a constant temperature of 20°C, employing measurement techniques of an earlier study at atmospheric pressure. The results show that, at a given frequency, a plot of molecular absorption versus humidity has a maximum value that is independent of pressure in the range of pressures from 0.4 to 1.0 atm. The effect of lowering the pressure is to shift the peaks in the curves of absorption versus humidity to lower values of relative humidity.