The mainstay of gene transfer studies is the use of wild-type cDNAs to effect phenotypic correction of diseases. However, this strategy is not feasible for genetic diseases caused either by mutations of large genes or by dominant-negative mutations, or where the regulation of the gene is critical. In this review, we will discuss a novel RNA reprogramming strategy - spliceosome-mediated RNA trans-splicing - where the pre-messenger RNA is modified by the splicing of two independent RNA species. The use of trans-splicing to effect phenotypic change in the hereditary bleeding disorder haemophilia A will be discussed.