8-Chloro-2′-deoxyadenosine (8-Cl-dAdo) was incorporated into synthetic DNA oligonucleotides to determine its effects on DNA synthesis by the 3′–5′ exonuclease-free Klenow fragment of Escherichia coli DNA Polymerase I (KF–). Single nucleotide insertion experiments were used to determine the coding potential of 8-Cl-dAdo in a DNA template. KF–inserted TTP opposite 8-Cl-dAdo in the template, but with decreased efficiency ...