The variation of current with magnetic field for constant applied electric field has been measured in thin films of InSb in which the transverse magnetic field is aligned both normal to and in the plane of the sample. These measurements have been performed for values of electric field both below and above that required for impact ionization of the lattice. The results are shown to be well explained by the magnetoresistance theories, of Wieder and Pikus, which indicate a maximum contribution of the surfaces to the measured magnetoresistance for a sample whose thickness is ∼1.4 times the bulk diffusion length. From the results it is estimated that the ratio of the recombination rates associated with the two surfaces of the films is ∼0.4, the larger recombination rate being associated with the free surface.