A parallel-aware program MPI_FSEARCH has been implemented to perform molecular replacement using an exhaustive six-dimensional search. In particular, the program can be used to deal with diffraction data at very low resolution (d > 10 A) that would normally not be appropriate for other molecular-replacement programs such as AMoRe and CNS. Although an envelope constructed from a PDB (Protein Data Bank) file was tested in the present study, the program can be used to perform low-resolution molecular replacement with an envelope derived from various sources such as electron microscopy or small-angle solution X-ray scattering.