A completely automatic high shear rate rotary viscometer has been developed. Continuous variation of speed allows instantaneous plotting of viscosity versus shear rate by means of a desk computer. Due to the short response time of the temperature control and to the optimum geometry of the viscometer, thermal corrections are not necessary over the whole range of viscosity. The instrument can deliver flow curves in fifteen minutes with an oil sample of 10 millilitres in the following test conditions: temperatures from 80 to 150°C, shear rates from 5 . 104 s−1 to 1.2 . 106 s−1. The repeatability of the apparatus is 2 to 3%.