<p>The present invention relates to the use of nucleoside derivatives of formula Iwherein B signifies a 9-purinyl residue B1 of formulaor a 1-pyrimidyl residue B2 of formulawherein the symbols are as defined in the specification,and of pharmaceutically acceptable salts thereof; for the treatment of diseases mediated by the Hepatitis C Virus (HCV), for the preparation of a medicament for such treatment and to pharmaceutical compositions containing such compounds.</p>
