This paper presents case studies for both rock mass modulus and rock mass shear strength in an attempt to assess the validity of the approach of using GSI and the Hoek-Brown criterion. It is concluded that for some rock masses the method works well, but in other cases can give very misleading assessments of stiffness and shear strength parameters. It is also concluded that further work is required in collecting and analysing good case studies in order to provide guidelines for the profession.