An experimental set-up for investigating macrosegregation formation due to deformation of an isotropic metallic mushy zone is presented. In the experiment, a semisolid Al-5.9wt%Cu sample is isothermally and non-uniformly compressed. Concentration and eutectic fraction are measured along selected lines, after quenching the sample. Results show that interdendritic liquid is pressed out of the central part of the sample to its outer part, increasing the concentration in this region. The experimental test is then addressed by a two-phase continuum model recently presented elsewhere. The modelling results show the same tendencies observed experimentally, although local variations in composition are not well correlated. Suggestions for future work are made.