Measurements were made on the effect of pressure on ultrasonic absorption in a 0.5Maqueous solution of manganese sulfate at 25°C. A cylindrical resonant cavity was used for obtaining absorption in the frequency regions of 300 and 500 kHz, at pressures up to 20 000 psi. Results are similar to those obtained forMgSO4, in that absorption decreases by a factor of about 3 for a pressure increase of 15 000 psi. Independent conductivity data show nearly the same behavior forMnSO4as forMgSO4solutions, namely, an increase of only about 14% in the concentration of dissociated ions for the same pressure increase. These results forMnSO4appear to be inconsistent with the model used by Atkinson and Kor to analyze their data. The large effect of pressure on ultrasonic absorption is similar to that observed by Carnevale for 0.1MMnSO4at 60°C from 9 to 75 MHz.