Progress in some areas of medical research is leading to larger and more complex therapeutic products - for example, cellular or gene therapies. For decades, the bioprocessing industry has relied upon column chromatography as the mainstay of purification processes. Whilst highly effective for the purification of proteins and smaller molecules, chromatographic techniques are not necessarily well suited to purification of these newer, larger targets. This article considers the approaches adopted in the purification of large, complex targets and emphasises the need for more focused development of purification techniques more suited to the target's size and complexity. (C) 2008 Society of Chemical Industry