Since first proposed by Zamencik & Stephenson in 1978 [1], anti-sense oligodeoxynucleotides (ODN) have been successfully used to inhibit/block the expression of specific genes. This process relies on the ability of an ODN to bind a complementary sequence of messenger ribonucleic acid (mRNA) and so prevent its translation [2]. The mechanism is believed to operate through steric hindrance, by RNase H-like cleavage, or through a combination of both [3]. In addition, formation of triplex DNA via Hoogsteen or reverse-Hoogsteen binding may also have 'anti-gene' activity [4,5]. In the last few years there has been increasing interest in technology which allows researchers to address questions about gene function, to inhibit specific intracellular molecules and to temporarily block specific gene effects without the need for 'knock-out' mice or neutralizing antibodies [6]. This technology may lead to new therapeutic approaches to the treatment of human diseases at a molecular level, and trials are in progress to evaluate their potential for clinical use [7-9]. There are many advantages to anti-sense therapy [2,6,10]. Provided that the relevant gene sequences are known, there is very wide choice of gene targets, including intracellular, membrane-bound and soluble molecules of mammalian cells, bacteria and viruses. In this issue of Clinical and Experimental Immunology, Ikizawa et al. [11] describe the use of ODN to block IL-4 receptor expression and IgE synthesis by peripheral blood B cells. This editorial assesses ODN and their therapeutic potential.