Isomorphous difference density maps Fo,n − Fo,1 (where n is the data-set number) around the four disulfide bonds present in lysozyme. Maps are shown for Fo,2 − Fo,1 (0.14 MGy), Fo,9 − Fo,1 (0.63 MGy) and Fo,15 − Fo,1 (1.05 MGy). Disulfide bonds are highlighted in yellow. Maps are contoured at +3σ (green) and −3σ (red). For Cys6–Cys127 the topmost part of the bond is Cys6, with the bottom being Cys127. The remaining bonds are positioned such that the label matches the residue positions in each figure, with the first to the left and the second to the right. Note that the dose indicated is the cumulative dose.