1. Introduction. The question of predicting what happens to an elastic column when it is compressed uniaxially has long been a subject of investigation (see [9,17] for a bibliography). We address here the compression problem for a circular cylinder of radius h of compressible hyperelastic material which satisfies appropriate ellipticity and growth hypotheses. We study the mixed displacement-traction boundary value problem for the deformation x of the column in which the compression ratio (ratio of deformed to undeformed length) is prescribed, the surface traction at its ends has no tangential component, and the lateral surface is specified to be stress free.Results on the compression of a circular cylinder of general compressible material have previously been obtained by Simpson and Spector. They gave a necessary and sufficient condition for the equilibrium equations of elasticity linearized about xA to have an axisymmetric or barrelling solution [17], and showed that such a solution does exist for materials with certain specific stored energy functions [17,19]. Analogous conditions have been obtained by Ogden [ 16] for the existence of planar solutions to the linearized equations for a rectangular column, and by Davies [9] who considered the two-dimensional case of an elastic rectangle and showed that this would always have a solution for a general class of materials.As in previous treatments of this and similar problems we first give conditions which ensure that for each compression ratio A 6 (0, 1) there is precisely one homogeneous solution xA to the nonlinear problem with diagonal gradient. These are stated in Sec. 2 and apply to columns of general constant cross-section. The stability of x^ (in a sense made precise in Sec. 3) is then investigated, and the Complementing Condition (cf. Simpson and Spector [20]) for the linearized problem is discussed.In Sec. 5, results of Ball [5] are used to rigorously obtain an equation for Abar, the compression ratio X at which x; can first cease to be a weak local minimum of the deformation energy with respect to barrelling perturbations. Section 6 contains a comparison of Abar with ABUC , the compression ratio corresponding to the onset of planar buckling of a column of square cross-section of side 2h . (Calculation