The relative information content of mass and velocity measurements for initializing low-frequency equatorially trapped waves is considered using analytical arguments and a numerical model For the Kelvin wave, mass and velocity data are equally useful, but this is not true for the Rossby waves. It is the relative amount of potential energy and kinetic energy possessed by equatorial waves that determines the relative usefulness of mass and velocity data for initializing these waves. The effects of dissipation on the adjustment process is considered. It is shown for the Kelvin wave that mass and velocity data are equally useful even when dissipation is present, but the Rossby wave adjustment is sensitive to the level and form of dissipation used.