The effects of temperature and humidity on the breakage propensity of two organic materials, Aspirin and sucrose, were investigated. The breakage propensities of both materials were found to be insensitive to humidity at ambient temperature; however they both showed a change in their impact breakage extent as a function of temperature, with Aspirin showing a more pronounced trend as compared to sucrose. Using the breakage data as a function of temperature, a lumped parameter, representing hardness, H, and fracture toughness and having the form H/K-c(2) according to the model of Ghadiri and Zhang [1], was evaluated as a function of temperature. The value of this parameter also showed an increase with temperature, indicating that the fracture toughness of Aspirin should decrease with an increase in temperature, considering the functional form of the parameter. In addition, its breakage propensity as a function of temperature was found to be well described by the Arrhenius equation from which the activation energy, -19.04 J/mol can be explained as equivalent to the energy required to overcome plastic deformation and initiate fracture. (C) 2010 Elsevier B.V. All rights reserved.