Pseudo first-order rate constants for the Zn2+-promoted cleavage of 15 different monophosphates, 4 different ribo homopolymers and RNA III from baker's yeast have been determined. Furthermore, the distribution of various nucleosides at the 3'-and 5'-terminus of the oligomeric hydrolysis products of RNA has been quantified. On these bases, the effect of nearest neighbours on the metal-ion-promoted hydrolysis of the internucleosidic phosphodiester bonds of RNA is discussed.