In the framework of the CEC Brite Euram programme on "Investigations on aluminium-lithium alloys for damage tolerant application", the NLR work in Task 3 concentrated on Fracture Toughness. In part I of the investigation residual strength tests were performed on 500 mm wide CCT panels of the Al-Li sheet alloys 2091-T84 and 8090-T81 and on 2024-T3 reference material. The test orientations were L-T, T-L and 60" to the rolling direction. Tests and analyses were carried out in accordance with the ASTM specification E561. Further, experimental details of ASTM E561 were examined in part II of the investigation. It was found that the fracture toughness as well as the yield strength of the Al-Li sheet alloys were significantly lower than those of 2024-T3. The most appropriate method for correction of experimentally determined compliances to enable use of the analytical compliance/effective crack length relation given in ASTM E561 is by adjustment of the E-modulus.