Although seismic tomography evidence leaves no room for fully layered mantle convection, it is still arguable that over Earth's history convection has efficiently homogenized mantle composition. We first searched for remains of the early differentiation of the planet in the 3.8 Ga rocks from Isua, Greenland. A sensitive indicator is the extinct radioactivity of 146Sm which decays to 142Nd with a half-life of 103 Myr. From the 142Nd excess of about +2 epsilon observed in chondrites (Prinzhofer et al., 1992) and differentiated meteorites (Nyquist et al., 1994), we can expect that differentiation events older than ca. 4.2 Ga left measurable isotopic effects in parts of the mantle. Three mafic samples from Isua analyzed by MC-ICP-MS in Lyon show a distinctive 142Nd anomaly of +0.3 epsilon unit, while all other samples are isotopically normal. Replicate values (2σ = 0.15 ǎrepsilon) show that they are significant and confirm the magnitude of the single anomaly found by Harper and Jacobsen (1992). At 3.8 Ga, some mantle domains had escaped full homogenization. We also searched for 142Nd anomalies in samples originating from parts of the mantle with a potentially primitive character. The isotopic composition of Nd has been determined on a number of samples from high 3He/4He volcanic centers (Iceland, Ethiopia, Loihi). Typical uncertainties of 15 ppm were obtained by at least three repeat analyses. Eight Icelandic samples and nine Ethiopia samples have normal 142Nd abundances. In contrast, 3 of 6 Loihi samples indicate 142Nd anomalies in excess of 0.5 ǎrepsilon. Replicate analyses of these samples are in progress. Excess 142Nd in the mantle source of Loihi basalts would signal the presence of pristine early mantle in the very same place where the O, Os, and Hf isotope systematics (Lassiter and Hauri, 1998; Blichert-Toft et al., 1999) seem to call for the recycling of material that formed in a low-temperature hydrous environment. In spite of active subduction down to the core-mantle boundary, the lower mantle appears to retain some primordial material as manifested by both high 3He/4He ratios and 142Nd anomalies.