Since long it is known that the strength of oxide ceramics and glasses is influenced significantly by the presence of water. This not only leads to a strength reduction but also to a strain-rate effect. Conventionally, these effects are explained by the reaction of water at the crack tip with the metal-oxygen bonds. Recently, it has been shown that also adsorption can play a significant role. The relevant experiments and modelling are discussed. Moreover, the influence of various other gases, like H2S, NH3, NO and CO, on the strength is discussed. For materials with a process zone the influence of the microstructure has to be taken into account. This behaviour is exemplified by a quast-brittle polymer composite using the fictitious crack model with a bi-linear softening model. Useful future extensions are indicated. (C) 2002 Elsevier Science B.V. All rights reserved.