A computer program has been developed to simulate the complicated electron diffraction patterns of alloys consisting of an underlying matrix phase in which are embedded various crystallographically oriented precipitates. These precipitates consist of different variants each with a specific orientation relationship to the underlying matrix. The program is designed to calculate the number of possible variants and the specific orientation of each variant using a general orientation relationship input by the user, usually in the form of an axis-angle pair or two parallel directions or planes. The program then plots the superimposed diffraction pattern of the matrix and all variants for a given zone axis of the matrix using the calculated orientation relationships of the variants. The crystal symmetries of the matrix and the precipitate phases are employed for the former, the Ewald-sphere concept for the latter. The program is also equipped with the option of displaying the indices and relative intensities of the screen-displayed diffraction spots. Necessary symmetry, atomic scattering and structural data required for the computations are incorporated into the program in the form of data files. The program developed has been tested for various common orientation relationships, e.g. b.c.c. and fc.c. twins, Bain, Kurdjumov-Sachs and omega, and some of the simulation results, in the form of variant transformation matrices and diffraction patterns, are presented.