  We present a rotationally invariant matrix product method (MPM) of isotropic
spin chains. This allows us to deal with a larger number of variational MPM
parameters than those considered earlier by other authors. We also show the
relation between the MPM and the DMRG method of White. In our approach the
eigenstates of the density matrix associated with the MPM are used as
variational parameters together with the standard MPM parameters. We compute
the ground state energy density and the spin correlation length of the spin 1
Heisenberg chain.
