Poly(vinylidene fluoride) films in ethyl acetate vapor were studied at 30 degrees C for vapor pressures of p = 0, 12, 30, 40, 66, 85 torr and elongations epsilon = 4.5%, 7%, 9.5%, 19%, 29%, and 44%. A cyclic experiment was also performed at epsilon = 7% and p = 40 torr for three sorption/desorption cycles. Assuming, as a first approximation, that the stress relaxation of the "dry" and "wet" polymers is proportional to the elastic strain, epsilon(el), empirical calculations were performed and compared to experimental results. In general, the presence of a vapor or gas in a polymer matrix enhances the stress relaxation by softening or plasticizing the polymer and transforming a portion of the elastic strain, epsilon(el), into the plastic strain, epsilon(pl). As the transformation continues, the sorption and stress of the wetted elongated sample change simultaneously with time until an optical "overshoot" and a mechanical or stress "undershoot" is observed. This result seems to be the consequence of the differential change of the stress of the "dry" and "wetted" samples with sorption time, tau = t - t(o)(t = time; t(o) = initial sorption time), which depends on the differential time dependencies of the transformations of the elastic and plastic strains.