A total of human or humanized 494 Fab structures are included. Triangles represent apo-Fabs (Fabs with no antigen bound) while squares represent holo-Fabs (Fab-antigen complexes). Ordinary structures are represented by small solid black marks (275 black squares for the most abundant group, holo-Fabs, and 164 black triangles for apo-Fabs). Clinically relevant structures (those identified in the structure title as humanized Fabs or as derived from clinical mAbs) are emphasized by using large unfilled red triangles for apo-Fabs (30 structures) and unfilled red squares for holo-Fabs (25 structures). Also plotted are the PDB’s four intact IgG antibodies (blue Y’s), and the Fab fragment structure reported in this paper, 5K8A (red unfilled oval). The plot shows the acceleration of the field, with about half the structures appearing in the past four years, and a trend toward study of clinically-relevant structures at high-resolution. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)