Sinking rates of natural fecal pellets from freshly collected euphausiids (126–862 m/day) were, in general, two to three times higher than the sinking rates of pellets produced by the same animals maintained on a diet of Artemia and algae (53–411 m/day). The difference is attributed to different degrees of compaction as well as different food residues in the two types of pellets. Sinking rates of natural fecal pellets from euphausiids can account for the rapid descent of radionuclides. Euphausiid fecal pellets may be at least as important quantitatively as sinking carcasses in the downward transport of matter to deep water and sediments.