A detailed study of strontium isotope variations in Neogene marine carbonate sediments from Deep Sea Drilling Project 590B, using techniques that allow the (super 87) Sr/ (super 86) Sr ratio to be determined to better than plus or minus 0.000 01, gives a high-resolution record of the Sr isotopic evolution of seawater. The data show that the rate of change of the marine (super 87) Sr/ (super 86) Sr ratio has varied significantly even on time scales as short as 1 m.y. Periods of particularly rapid growth appear to follow major marine regressions and probably reflect an increase in the delivery of radiogenic Sr from the continents coupled with a decreased submarine carbonate dissolution rate (greater carbonate compensation depth). Periods of relatively slowly changing (super 87) Sr/ (super 86) Sr follow major marine transgressions. On the basis of correlations with the marine oxygen isotope record and the times of major continental glacier growth, it is inferred that the effects of sea-level variations are modified by climatic factors that affect the intensity of continental weathering and runoff. The effects of sea-floor generation rate variations are not discernible for the Neogene. The maximum attainable stratigraphic resolution using Sr isotopes is between 0.1 and 2 m.y. for this time period.