  The critical temperature of a three-dimensional Ising model on a simple cubic
lattice with different coupling strengths along all three spatial directions is
calculated via the transfer matrix method and a finite size scaling for L x L
oo clusters (L=2 and 3). The results obtained are compared with available
calculations. An exact analytical solution is found for the 2 x 2 oo Ising
chain with fully anisotropic interactions (arbitrary J_x, J_y and J_z).
