[en] The effect of crack length on fracture toughness and the crack growth resistance curve were determined for CT specimens of the titanium alloy Ti--6Al--4V. The crack growth resistance curve rises steeply up to a crack extension of 0.4 mm. It is possible to determine fracture toughness according to the ASTM standard method with sufficient accuracy in a range 0.3 < a/W < 0.7. It is possible to evaluate the crack extension from the deviation from the linear part of the load crack opening displacement curve or from the slope of the unloading curve for delta a > 0.5 mm with an accuracy of about 20%