The charge and spin density distributions in antiferromagnetic Cr-Al solid solutions have been studied by means of X-ray and neutron diffraction experiments on powdered samples. The results show that the valence electrons of aluminium in the alloys must be localized so that they behave rather like 3d electrons having T_2g type symmetry. The departure from spherical symmetry of the spin distribution around the magnetic atoms is not large, but shows a tendency to become more E_g like with increasing aluminium content. These results suggest that the increase in magnetic moment with increasing aluminium content cannot be simply due to aluminium electrons filling the chromium d band. It is suggested that the change in magnetic properties is mainly due to a decrease in the chromium bandwidth relative to the exchange energy as the amount of d shell overlap is reduced by adding aluminium.