AbstractIn order to get information on the bioactive conformations of the endogenic renin substrate, a few peptide segments of angiotensinogen, along with a pepstatin analogue, were studied in the solid state by x‐ray crystallography. These results are compared with the conformations of acidic proteinase inhibitors observed at the level of the active site. Such a comparison allows us to point out some analogies and differences between the observed conformation for the peptide alone and the conformations on the active sites. The analysis of the results should be a good starting point for making hypotheses on the renin substrate bioactive conformation(s