A new method for the preparation of aromatic, S-substituted derivatives of N-acetyl-L- cysteine is described. The method involves nucleophilic substitution of aromatic iodides by N-acetyl-L- cysteine in the presence of copper(I) iodide, and provides the first example of nucleophilic substitution of unactivated aromatic halides by N-acetyl-L- cysteine . The method has been used to prepare N-acetyl-S-(2-thienyl)-L- cysteine and N-acetyl-S-(3-thienyl)-L- cysteine from 2-iodothiophen and 3-iodothiophen respectively. In addition, the method has been successfully applied to iodobenzene and 1-iodonaphthalene. A product yield of about 30% was obtained in each case.