Laboratory-accelerated degradation tests have been conducted to understand the stability of high tenacity poly(ethylene terephthalate) (PET) as a result of exposure to stressful chemical environments when used as an implantable prosthesis. The experiments were conducted at 40 degrees C to mimic normal physiological conditions. At various time intervals, samples were collected and evaluated for weight loss (%), mechanical properties, and changes in the surface structure. The mechanical properties that were specifically observed include: breaking load, tenacity, breaking strain, work of rupture, and modulus. For all PET fibers loss of work of rupture was the highest. An empirical formula was developed to estimate degradation behavior over time, though such a prediction cannot be verified without further research and observation. The transverse cracks formed on the stressed samples beyond the critical load in an alkaline environment at 40 degrees C are similar to those found on the PET prosthetic grafts. The cracks in the experimental samples at 40 degrees C and those recovered from human bodies both appear more 'corallite in structures' versus those at room temperature. Therefore, it is concluded that the arterial stress that the PET prosthetic graft encountered inside the human body was higher than the yield load of the fiber. (c) 2006 Wiley Periodicals, Inc.