Isotope dilution concentration determinations are accurate to approx. 1% for Rb and Sr, and 0.5% for Sm and Nd. Total procedural blanks averaged apporx. 1 ng for Sr and 100 pg for Nd, during the study period. Measured 87Sr/86Sr ratios were analyzed using four-collector static mode measurements. Thirty measurements of SRM-987 during the study period yielded mean 87Sr/86Sr=0.71032±2. Measured 143Nd/144Nd normalized to 146Nd/144Nd=0.7219. Analyses were dynamic mode, three-collector measurements. Thirty three measurements of the La Jolla Nd standard during the study period yielded a mean 143Nd/144Nd=0.511838±8 (2sigma mean). e-Nd values are calculated using a present-day 143Nd/144Nd (CHUR)=0.512638.