A new microcomputer‐controlled instrument has been developed for making measurements of thermomechanical behavior of polymeric fibers and yarns under conditions relevant to high‐speed industrial fiber processing. The instrument can apply extension and/or twist, and rapid heating or cooling in the temperature range 20–300 °C, while tension and torque are measured. Particular novel features are: a temperature control device providing heating or cooling at rates up to 103K/s; a new form of high‐sensitivity torque transducer with resolution of 10−9Nm; and computer integration of extension, twist, and temperature. The instrument provides an unprecedented degree of flexibility in the design of thermomechanical tests. It is suitable not only as a versatile research tool for material property measurements relevant to processes such as spinning, heat setting, and thermobonding of fibers, but also as a convenient tester for use in quality control on fibers and yarns.