In 1984 Mario Geysen and his colleagues described a technique for the simultaneous synthesis of hundreds of peptides on polyethylene rods. The peptides, still on the rods, could be used directly in enzyme-linked immunosorbent assays (ELISAs) and in this way linear parts of B-cell epitopes could be mapped. For the analysis of T-cell epitopes, peptides can be cleaved from the rods and incorporated into proliferation assays. This method, called the 'Pepscan' procedure, has been used for the detailed characterization of epitopes of viruses, Chlamydia and Mycobacteria: it is a powerful new approach to the epitope mapping of parasite proteins.