The effects of neutron flux anisotropy upon thermal-neutron flux perturbations were found by experimentally determining the perturbations induced by foils placed in fluxes of known nonuniformities. Anisotropies in the magnitude of the vector flux were introduced by placing a ‘black’ cadmium absorber sheet in an isotropic flux produced by a uniform slowing-down source in water. The resulting angular and spatial distributions of the thermal-neutron flux were computed by using Yvon's method to solve the Boltzmann equation for an absorbing half space containing a uniform slowing-down source. Using indium foils with thicknesses from 14 mg/cm2 to 184.9 mg/cm2, the relative flux perturbations were measured to within ±1% in regions which varied from a highly directional flux at the cadmium surface to essentially an isotropic distribution several mean free paths from the absorber. The experimental data indicated that the flux perturbations remained constant at all distances greater than about three mean free paths from the non-reentrant boundary, but that the flux depression decreased in the region near and vanished at the boundary. It was concluded, contrary to earlier predictions, that flux perturbation theories, based upon isotropic flux models, cannot be used to correct flux perturbations induced in all anisotropic fluxes. It was pointed out that, if this effect is overlooked, significant errors may exist in some relative or absolute flux measurements made in the region near a boundary or absorber.