Various methods for the evaluation of the critical J-integral J(Ic) based on the standard ASTM E813-89 are analyzed by conducting investigations on a ductile medical grade ultra high molecular weight polyethylene (UHMW-PE) at room temperature. Differences in J(IC) reaching almost 50% were recorded between the methods investigated. The controversy surrounding the construction of the crack blunting line is discussed in terms of the stretch zone width together with the size requirements of ASTM E813-89. The findings of this investigation suggest that an R-curve construction based on mid-thickness crack growth and ultimate tensile strength (UTS) combined with a blunting line of slope m = 2 and modified exclusion lines provides consistent and conservative J(Ic) values. Using this technique, a near plane strain value, smaller than previously published data, of 66.5 kJ/m(2) was obtained at 23 degrees C.