In the surface harmonics method, to derive the finite-difference equations for a heterogeneous reactor the neutron flux distribution and neutron importance distribution in each cell of the reactor are represented as a linear combination of some trial functions. Reciprocity relation between neutron distribution and neutron value at the cell boundary is necessary to prove the adjointness of the finite-difference equations. In this paper we present this reciprocity relation for two-dimensional geometry with the use of eight trial functions.