The influence of fluoride (F⁻), bromide (Br⁻), iodide (I⁻), thiocyanate (SCN⁻) and nitrite (NO₂⁻) on the reaction of a myeloperoxidase–H₂O₂–Cl⁻ system with a nucleoside mixture was studied. The reaction was carried out under mildly acidic conditions and terminated by N-acetylcysteine. Without the additional anions, quantity of nucleosides consumed fell in the following order: 2′-deoxyguanosine>2′-deoxycytidine>>2′-deoxythymidine>2′-deoxyadenosine≈0. F⁻ did not affect the reaction. Br⁻ increased the consumption of 2′-deoxycytidine and 2′-deoxythymidine, but decreased that of 2′-deoxyguanosine. I⁻, SCN⁻ and NO₂⁻ suppressed the reaction. These results suggest that Br⁻ has a unique effect in relation to nucleoside damage caused by myeloperoxidase.