MOLREP is an automated program for molecular replacement which utilizes effective new approaches in data processing and rotational and translational searching. These include an automatic choice of all parameters, scaling by Patterson origin peaks and soft resolution cut-off. One of the cornerstones of the program is an original full-symmetry translation function combined with a packing function. Information from the model already placed in the cell is incorporated in both translation and packing functions. A number of tests using experimental data proved the ability of the program to find the correct solution in difficult cases.