We have investigated the effect of the bovine serum albumin (BSA)-catalyzed ortho rearrangement of synthetic and enzymatically generated N-(sulfooxy)-2-fluorenylacetamide (NSF) to the O-sulfate esters on the binding of NSF to transfer ribonucleic acid (tRNA) and to deoxyribonucleic acid (DNA). Binding of synthetic NSF to tRNA and DNA decreased ~90 and 70%, respectively, in the presence of BSA. Under these conditions, the ortho rearrangement, a minor reaction in the absence of BSA, was nearly quantitative. The decrease of adduct formation to nucleic acids was not attributable to the competitive binding of NSF to BSA. Binding of NSF, generated by cytosolic sulfonation of the arylhydroxamic acid, N-hydroxy-2- fluorenylacetamide, to tRNA, was diminished ~97% in the presence of BSA while the ortho rearrangement of the sulfonated substrate increased from <0.5% to ~50%. Adduct formation of DNA with N-hydroxy-2-fluorenylacetamide, activated by enzymatic sulfonation, was inhibited ~90% in the presence of BSA. In these experiments, the catalytic effect of BSA on the ortho rearrangement of enzymatically sulfonated N-hydroxy-2-fluorenylacetamide was of the same order as observed in the experiments with tRNA. The data obtained on the covalent interaction of DNA with enzymatically activated N-hydroxy-2-fluorenylacetamide indicate that, in addition to NSF, another electrophilic species accounts for binding of activated N-hydroxy-2- fluorenylacetamide to DNA. The data support the view that the reactive electrophile is N-acetoxy- 2-fluorenamine, resulting from the N,O-transacetylation of N-hydroxy-2-fluorenylacetamide. In the presence of BSA, adduct formation of N-acetoxy-2-FA with tRNA and DNA was decreased by 81 and 66%, respectively. The mechanism for the inhibition of binding of N-acetoxy-2-FA to nucleic acids remains to be determined.