Fracture studies of components involving mode III loading are rare. This paper concentrates on mixed-modes I, II and III fracture testing of brittle PMMA material and summarises an extensive experimental investigation. Karpour and Zarrabi have developed a special pair of grips for which they have received a patent. These grips allow the application of various mixtures of modes, including mode III, using a universal testing machine. To measure the three-dimensional crack-tip opening and sliding displacements, Karpour and Zarrabi have also developed a novel stereo machine vision system whose description is included in the paper. The measured critical crack-opening displacements presented in normalised format with potential of being used to assess the integrity of any component against elastic fracture and they compare well with limited pertinent data available from literature. © (2011) Trans Tech Publications, Switzerland.