The effect of nontidal ocean mass loading is investigated as a possible cause for the seasonal variability observed in the vertical components of the GPS-derived site coordinates of tropical Pacific islands. The nontidal ocean mass origin sea level changes (MOSLCs) are estimated by subtracting the steric height changes observed at buoys from the net sea level changes measured by satellite altimetry. Assuming a linear relationship between the MOSLCs at the closest buoys and the GPS vertical movements, the coherences and the admittances are estimated. We found evidence that the vertical movements are caused by the loading effect at three out of four sites. The occasional deviations between the vertical movements and predicted loading deformations are presumably due to the invalidity of the assumption of a linear relationship between the MOSLCs and the loading deformation and/or of the mean temperature-salinity relationship used in estimating steric heights in the corresponding periods.