MOST of the helium-3 in oceanic sediments comes from interplanetary dust particles (IDPs), and can therefore be used to infer the accretion rate of dust to the Earth through time(1-3). He-3 records from slowly accumulating pelagic clays indicate that the accretion rate varies considerably over millions of gears, probably owing to cometary and asteroidal break-up events(3). Muller and MacDonald have proposed(4) that periodic changes in this accretion rate due to a previously unrecognized 100-kyr periodicity in the Earth’s orbital inclination might account for the prominence of this frequency in climate records of the past million years(5). Here we report variations in the He-3 flux to the sea floor that support this idea, We find that the flux recorded in rapidly accumulating Quaternary sediments from the Mid-Atlantic Ridge oscillates with a period of about 100 kyr. We cannot yet say, however, whether the 100-kyr climate cycle is a consequence of, a cause of, or an effect independent of these periodic changes in the rate of delivery of interplanetary dust to the sea floor.