The program SIR2000 [Burla et al. (2000). Acta Cryst. A56, 451-457] was des
igned for the ab initio solution of macromolecular crystal structures, prov
ided that the data resolution is no lower than 1.2 Angstrom. As the phasing
procedure of SIR2000 is rather time consuming, modifications have been int
roduced to improve its efficiency and to make it additionally suitable for
small molecules (new version SIR2000-N). The role of the tangent refinement
in modern phasing procedures is enlightened.