A comparison is presented of six methods involving nitric acid in conjunction with other reagents to digest three certified marine biological samples (DOLT-3, DORM-3, IAEA-407) and a fish bone homogenate (prepared from Merluccius australis). An inductively coupled plasma-mass spectrometer with an octopole collision cell was used to determine up to 40 elements (Li, B, Na, Mg, Al, K, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Y, Ag, Cd, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Pb, Th, U) in the digests. These results were assessed in terms of their accuracy and precision, and a flow chart was developed to aid the selection of the optimal digestion method. Although none of the methods was found to give accurate determinations for all elements in the different reference materials, a relatively simple method involving nitric acid and hydrogen peroxide heated in a domestic microwave oven gave the most acceptable results.