Geoid heights derived from the Geos 3 satellite altimeter show relatively short wavelength (λ ≲ 280 km) geoid highs of 5--12 m over the crest of the Hawaiian-Emperor seamount chain and geoid lows of 1--3 m over flanking regions. These geoid undulations can be generally explained by a simple model in which the load of the seamount chain is supported by a strong, rigid lithospheric plate. The best fitting estimates of the effective elastic thickness of the plate based on data over the Hawaiian Ridge are in the range 25--37.5 km. The elastic thickness cannot be reliably determined from altimeter data over the Emperor Seamounts, although it is probable that it is significantly lower than that obtained for the Hawaiian Ridge. These estimates of the differences in elastic thickness along the seamount chain are in general agreement with previous studies along the chain and provide useful new constraints on the long-term (>106 years) mechanical properties of the oceanic lithosphere.<