Dear All, In the on-line phenix document, there is, "Should I use the MTZ file output by phenix.refine as input for the next round of refinement? The only time this is necessary is when you refined against a dataset that did not include R-free flags, and let phenix.refine generate a new test set. In this case, you should use the file ending in "_data.mtz" for all future rounds of refinement. You do not need to update the input file in each round, as the actual raw data (and R-free flags) are not modified". When we have phenic adding R-free flgas in the first time we process the mtz data by phenix.refine, besides the *data.mtz, phenix also create a *.mtz. In the future phenix.refine, can I refine by always using the *.mtz created in the R-free flag adding step, rather than refine by always using the *data.mtz created in the R-free flag adding step? What is the difference between that *data.mtz and that *.mtz? And what is the side-effect if in the future steps I refine by always using the *.mtz created in the R-free flag adding step? Best regards. Smith