This paper describes an apparatus for applying simultaneously or alternately forced vibrations in tension and torsion on viscoelastic samples. The measurements can be made on unstrained or strained samples within a frequency range from 0.01 to 10 Hz. The temperature control of the sample is achieved either in an air circulating chamber or in a liquid environment. Typical results of measuring the dynamic moduli of a carbon black filled rubber in tension and shear are presented. The complex Poisson's ratio of filled rubber was calculated from its dynamic moduli as a function of strain. © 1969 The American Institute of Physics.