OP-Rheometer is a rotational viscometer of concentric type, which was developed to measure blood viscosity at low shear rate (0.2-40 sec-1) and viscoelasticity at 0.1-3.0 Hz in the context of clinical medicine. This system consists of a mechanical unit, a control unit (console), a data processing unit and a printer. The dynamic or steady state flow data are automatically printed out. An outer cylinder (sample container) is connected to a torsion wire assembly supported by a pair of magnetic bearings. The angular displacement is detected by a pair of variable differential transformers. In clinical application of this rheometer, authours have confirmed that the viscosity and viscoelasticity of blood from diabetic patients are higher than for normal subjects.