A magnetic sphere or needle rheometer which may be fully controlled by a personal computer is provided. The rheometer is capable of measuring viscosities in the range of 5.times.10.sup.-4 to 5.times.10.sup.4 Pas (0.5 cP to 5.times.10.sup.7 cP). It can operate at shear rates between 1 s.sup.-1 and 2.times.10.sup.-4 s.sup.-1 and measure relaxation times down to 100 ms. The rheometer includes a magnetic coil which is used to maintain the sphere or needle in a selected position within a sample cell. The current required to maintain the sphere or needle in this position as the sample cell is moved up or down is measured. The viscosity of the liquid can be calculated from the difference in current flowing through the coil when the cell is stationary and when it is moved at a constant velocity.