Radiocarbon dates from fossil oyster beds of intertidal origin on Magnetic Island, north Queensland indicate that the local Holocene maximum of relative sea level was attained no later than 5660 + or - 50 B.P. (conventional uncorrected age) and remained at 1.6-1.7 m above modern levels until 4040 + or - 50 B.P. Given the tectonic stability of the area, this implies that eustatic sea level remained at its Holocene peak for at least ca. 1600 yr. The new high-precision sea-level data indicate sea levels 1-5 m higher than those of the same age inferred from buried mangrove deposits on the inner shelf in north Queensland, Uncertainties in deriving relative sea level from such mangrove deposits may be a significant source of error in worldwide attempts to distinguish the eustatic and crustal warping components of relative sea-level change, especially in the tropics.