An experimental and numerical study was performed to ascertain the influence of V-notches on the strength of different brittle materials. Critical loads were computed using the cohesive process zone model that allows extension of classical methods, based on linear elastic fracture mechanics, to rounded V-notches and contained plasticity. A large experimental programme, with more than one hundred tests, was performed with PMMA samples to support the numerical predictions. All the experimental results are reported. In addition, experimental results of notched steel samples, performed by Strandberg, [Engng. Fract. Mech. 69 (2002) 403], and notched samples made with expanded PVC foams, performed by Grenestedt, Hallstrom and Kuttenkeuler [Engng. Fract. Mech. 54 (1996) 445], are in very good agreement with the numerical computations, adding further support to the cohesive process zone model. (C) 2003 Elsevier Science Ltd. All rights reserved.