Abstract A three-dimensional finite element investigation was made by the Bureau of Mines of the effect of insert materials on the elastic behavior of a cylindrical specimen loaded axially between rough end-plates. A constant displacement was applied to the end-plates. It is shown that the stress and displacement distribution normally existing within a specimen compressed axially between rough end-plates can be drastically altered when a low-modulus insert material is interposed between the specimen and the end-plates. The use of a low-modulus insert such as rubber ( E ≌4 × 10 3 psi, ν ≌ 0·45) develops large radial and tangential tensile stresses (on the order of one-half the applied axial compression near the specimen insert boundary) within the specimen. The existence of large, radial and tangential tensile stresses can influence the deformational behavior of a test specimen deformed under uniaxial loading. It is shown that the magnitudes of the induced stresses are very sensitive to both the ν/ E and L/ D values of the insert material. The conclusion of this study is that insert materials with ν/ E values larger than the ν/ E value of the specimen should be avoided in laboratory testing of specimens between rough end-plates.