Analyses for value assignment in the renewal Standard Reference Materials® SRM 1598a Animal Serum and SRM 1577c Bovine Liver included extensive characterization by neutron activation analysis (NAA). Conventional instrumental NAA procedures were complemented by pre-irradiation chemical separations for the determination of Al, V, Mn, and Cu, radiochemical separations for the determination of Ag, As, Cd, Cr, Cu, Mo, Sb, and Se, and the use of (anti-) coincidence gamma-ray spectrometry systems for the instrumental determination of Ag, Cr, and Hg. The previous materials, SRMs 1598, 1577, and 1577b, were analyzed together with the new materials for quality control.