There is described a method of synthesizing a family of oligopeptides of predetermined amino acid sequence, which together make up from 7 amino acids to the complete amino acid sequence of a target protein, which comprises: synthesizing a nucleic acid construct which codes for a fusion protein composed of overlapping peptides derived from the desired portion of the target protein, interspersed with regions which code for protease cleavage sites, expressing the nucleic acid construct in a suitable expression vector, harvesting the fusion protein corresponding to the nucleic acid sequence, and digesting the fusion protein with a protease selective for the cleavage sites to generate the oligopeptides. The oligopeptides may be generated in vitro or in vitro and may be used as vaccines against viral infections and in epitope mapping. MGGKWSKSSVVGWPAVRERMIEGRVGWPAVRERMRRAEPAADGVIEGRRRA EPAADGVGAVSRDLEKHIEGRGAVSRDLEKHGAITSSNTAAIEGRGAITSS NTAATNADCAWLEAIEGRTNADCAWLEAQEEEEVGFPVIEGRQEEEEVGFP VTPQVPLRPMTIEGRTPQVPLRPMTYKAAVDLSHFIEGRYKAAVDLSHFLK EKGGLEGLIEGRLKEKGGLEGLIHSQRRQDILIEGRIHSQRRQDILDLWIY HTQGYIEGRDLWIYHTQGYFPDWQNYTPEIEGRFPDWQNYTPEPGVRYPLT FGIEGRPGVRYPLTFGWCY