Ultralow frequency (ULF) magnetohydrodynamic pulsations (periods between 10 and 20 min) were observed on July 8--11, 1979 as Voyager 2 traveled through the middle magnetosphere of Jupiter between radial distances of 10 RJ and 35 RJ. The particle and magnetic pressure perturbations associated with the waves were anticorrelated. The electron and ion perturbations on the dayside were in phase. The pressure perturbations occurred both within and outside of the plasma sheet. Perturbations in the transverse components of the magnetic field were associated with the compressional perturbations but the transverse power peaked within the plasma sheet of Jupiter and diminished rapidly outside of it. The absence of finite gyroradius effects in the energetic ion (assumed to be protons) count rates points to perpendicular wavelengths longer than 0.8 RJ. If the pressure perturbations were caused by a convected structure nearly stationary in the plasma rest frame, the azimuthal wavelength was about 2 RJ. A conceptual model of the waves that accounts for the structure of the field and particle observations in the middle magnetosphere of Jupiter is presented. ¿ American Geophysical Union 1989