The capacity of Escherichia coli poly(A) polymerase to adenylylate the 3′‐OH residue of a variety of nucleosides, nucleoside 5′‐phosphates and dinucleotides of the type nucleoside(5′)oligophospho(5′)nucleoside is described here for the first time. Using micromolar concentrations of [α‐32P]ATP, the following nucleosides/nucleotides were found to be substrates of the reaction: guanosine, AMP, CMP, GMP, IMP, GDP, CTP, dGTP, GTP, XTP, adenosine(5′)diphospho(5′)adenosine (Ap2A), adenosine (5′)triphospho(5′)adenosine (Ap3A), adenosine(5′)tetraphospho(5′)adenosine (Ap4A), adenosine(5′)pentaphospho(5′)adenosine (Ap5A), guanosine(5′)diphospho(5′) guanosine (Gp2G), guanosine(5′)triphospho(5′)guanosine (Gp3G), guanosine(5′)tetraphospho(5′)guanosine (Gp4G), and guanosine(5′)pentaphospho(5′)guanosine (Gp5G). The synthesized products were analysed by TLC or HPLC and characterized by their UV spectra, and by treatment with alkaline phosphatase and snake venom phosphodiesterase. The presence of 1 mm GMP inhibited competitively the polyadenylylation of tRNA. We hypothesize that the type of methods used to measure polyadenylation of RNA is the reason why this novel property of E. coli poly(A) polymerase has not been observed previously.