The dynamics of deformation in cylindrical liners are studied experimentally and theoretically in -pinch geometry, where the cylinders are deformed by a magnetic field created by a current flowing along the axis. This method allows one to obtain one-dimensional deformation and a reliable recording of magnetic field and cylinder deformation. The experiments are performed with a current amplitude of 0.8 - 3 MA and a current rise time of 2.5 - . Aluminium and copper tubes, from 4 to 6 mm in diameter and 0.25 - 1 mm wall thick, are compressed. The deformation rates under study are in the range of . The time dependence of the radii of the copper and aluminium tubes are measured with a streak camera and by the pulsed x-ray technique. The time resolution of the streak and x-ray photographs is 10 - 15 ns, their spatial resolution is . A rheological model describing the dynamics of compression is developed. The model includes the description of the metal as a plastic medium with moving dislocations in the solid state, and as a viscous medium in the liquid state. The one-dimensional solution to magneto-hydrodynamical equations of the liner dynamics is compared with the experimental results and thus the following rheological parameters of the metal are obtained: , the probability of dislocation generation in plastic deformation; and , the drag stress, the parameter which characterizes a drag force acting on the dislocation.