The ratio of anhysteretic remanent magnetization (ARM) to magnetic susceptibility (&khgr;) is widely used for rapid estimation of magnetic grain-size variations. On interpreting ARM/&khgr; variations, no significant influence of interactions among magnetic grains on ARM acquisition is usually assumed implicitly, although some previous experiments using artificial sediments and biogenic magnetites opposed this assumption. Our rock-magnetic study of deep-sea surface sediments from the Pacific ocean showed that ARM/&khgr; depends strongly on &khgr;, the concentration of magnetic minerals, and on the R value of Cisowski [1981>, an index of the strength of magnetic interactions. This result demonstrates that ARM/&khgr; can be influenced significantly by magnetic interactions in natural sediments. We corrected for the influence of the magnetic interactions using the observed concentration dependence of ARM/&khgr;. Regional variations of ARM/&khgr; values before the correction were geologically unnatural in terms of magnetic grain-size variations. Previous interpretations of ARM/&khgr; variations on magnetic grain-size without consideration of magnetic interactions may not be valid.¿ 1997 American Geophysical Union