Static compression measurements to 60 GPa yield a room temperature isotherm for MnO that is described by a bulk modulus and pressure derivative K0=162(¿17) GPa, K0'=4.8(¿1.1). These values are compatible with ultrasonically determined moduli, and our data show that an Eulerian rather than a Lagrangian finite-strain equation of state is preferable. We find no indication of a structural transition to 60 GPa. Hence we interpret the variation of c44 with pressure that has been observed ultrasonically as reflecting magnetic interactions between Mn ions. A simple model of these interactions yields pressure derivatives c44'~0.1 and c44'≲-0.03 GPa-1, which are close to the ultrasonic values. ¿ American Geophysical Union 1987