A suite of lavas from Kosrae, Ponape and Chuuk islands, which are related to the Caroline hotspot, are characterized for Sr, Nd, Pb, Hf and He isotopic compositions and major and trace element concentrations. The observed radiogenic isotopic variability spans a relatively narrow range for 87Sr/86Sr (0.703171 to 0.703491), 143Nd/144Nd (0.512923 to 0.512991), 176Hf/177Hf (0.283075 to 0.283123), 206Pb/204Pb (18.357 to 18.839), 207Pb/204Pb (15.485 to 15.546), and 208Pb/204Pb (38.211 to 38.700). The 3He/4He data, collected by vacuum crushing of olivine, vary from 7.6 to 12.8 Ra, and are 7.8 Ra and 10.4 Ra in two peridotite xenoliths from Kosrae and Ponape, respectively. The three highest 3He/4He values (12.8, 11.5 and 11.3 Ra) were obtained from Kosrae lavas, and 3He/4He exhibits positive covariation with 87Sr/86Sr. This observation, together with low 3He/4He in a single fusion measurement of crushed olivine powder from the highest 3He/4He lava, supports a magmatic origin for the highest 3He/4He value of 12.8 Ra. As the high 3He/4He mantle domain is thought to reside in the deep mantle, the discovery of moderately high 3He/4He (i.e., 3He/4He greater than the mean MORB value of 8.8±2.1 Ra) in Caroline lavas complements a recent report of a seismically-resolved mantle plume conduit beneath the Caroline hotspot.Lavas with moderately elevated 3He/4He (up to 12.8 Ra) from Kosrae, as well as lavas from other high-3He/4He localities globally, exhibit evidence for a recycled oceanic crust signature, including elevated Ti concentrations and moderately radiogenic Pb isotopic compositions. This observation suggests that primitive high-3He/4He and recycled reservoirs are intimately associated, and mix, in the deep mantle sources of plumes. Hybrid mantle domains generated in this way serve as the melt source for lavas with elevated 3He/4He from many hotspot localities. Thus, the geochemistry of much of the mantle, including the high-3He/4He domain, may be modified by the addition of subducted materials.