Two methods commonly used to measure the durability of adhesive bonded joints, namely the lap shear joint and the wedge test, are compared for carbon fibre reinforced epoxy matrix composite. For unaged joints, where bond strength varies due to surface contamination, it is shown that lap shear strength and initial crack length are related when failure is interfacial between adhesive and adherend. When these joints are used for durability testing, by exposure to constant hot/wet laboratory conditions, the results do not appear to be comparable because the changes measured are attributable to changes in the adhesive properties rather than in the adhesive-adherend interfacial region. The lap shear strength can be related to the calculated moisture content and distribution in the joint.