Using the bond-fluctuation model, the conformational, energetic, and entropic changes of a single polymer chain caused by cyclic deformation is studied. The drawing velocity is varied by means of different relaxation times between deformation steps. The simulated temperatures reach from far above the Theta temperature to well below. Above the Theta temperature, the deformation is homogeneous and controlled by the entropy. No differences between loading and unloading can be seen. All simulations appear to be in equilibrium conditions. Below the Theta temperature, the deformation behavior for fixed drawing velocity is found to be completely different. Nonequilibrium effects show up. In the cyclic deformation, a hysteresis in the total force as well as in its energetic and entropic parts occur. A quasi reversible behavior of the globule-strand system in further cycles is described. (C) 2000 American Institute of Physics. [S0021-9606(00)50815-0].