Die compaction of powders is related to the principles of powder mechanics. Measurements are reported of boundary normal stresses occuring during one-sided die compaction of a fine ferric oxide powder. One series of experiments is carried out with carefully cleaned die walls, another series is performed with lubricated dies. The powder yield locus and wall yield loci are determined respectively with the help of a triaxial cell and a powder/wall friction apparatus. For both series of experiments the powder yield locus lies above the wall yield locus. The experimental data give support to the assumption that the stresses at the die wall obey the wall yield locus. With respect to the internal stresses of the powder, evidence is obtained that the powder yield criterion is not fulfilled, at least not necessarily.