It is shown that extended irreversible thermodynamics provides a natural scheme for describing viscoelastic bodies. This is achieved by introducing the inelastic stress tensor as variable in complement of the standard variables. The Poynting-Thomson, Maxwell, and Kelvin-Voigt models are recovered as particular cases of the formalism. Nonlinear and more complicated models, like Jeffreys' model, are also suggested. Propagation of plane harmonic waves and the consequences of the application of external sinusoidal solicitations are investigated. Finally, a comparison with some other theories is made. © 1988 American Institute of Physics.