A method is presented for studying bonded assemblies under pure mode III loading. It is based upon a novel fixture that can be mounted on a common universal testing machine and is able of realizing pure anti-plane shear conditions. Twisting of the bonded assembly generates a smoothly propagating circular crack front that allows for accurate measurements during the test. Data reduction is carried out based on the global load–displacement response and material properties are identified. Results are presented that demonstrate the capabilities of the proposed approach to provide mode III fracture parameters of adhesively bonded joints.