Voids created during neutron irradiation lead to volume welling and changes in the elastic properties of metals. Present theoretical treatments of the effect of voids on elastic constants do not consider the possible effect of gas pressure or surface stresses within the voids. These corrections have been determined for the change in bulk modulus. Although parameters required for numerical evaluation are not available for materials of technological interest (e.g. stainless steels), values for copper indicate that various correction terms tend to cancel. Thus, gas pressure should not be important in predicting elastic property changes caused by voids, and conversely, experiments involving elastic property measurements are impractical as a method to determine gas pressure within voids.