A suite of computer programs (REPLACE) for crystal-structure determination by the molecular-replacement method has been developed. It currently includes a general (locked) rotation-function program (GLRF) and a translation-function program (TF). The rotation-function program can carry out ordinary as well as locked self- or cross-rotation-function calculations. It can also optimize non-crystallographic symmetry parameters based on the maximal electron-density overlap of the subunits related by the non-crystallographic symmetry. The translation search can be based on R-factors, correlation coefficients, Patterson correlation and electron-density-correlation criteria. The packing of the molecular structure in the unit cell can be checked as well.