The Theological properties of magnetorheological suspensions (MRS) are investigated in a wide concentration range of particles of the disperse ferromagnetic phase in the presence of a magnetic field. It is shown that, along with an increase in the concentration of ferromagnetic particles, the range of control of the viscous stress increment in an MRS can be broadened by changing the size and shape of the ferromagnetic particles, introducing nonmagnetic particles into the dispersion medium as well as by heating the medium to the Curie temperature.