Antisense technology has been used for several years to "knock down" the expression of specific genes in living tissues to study the functions of their protein products. Specifically designed antisense oligonucleotides (ODNs) are short lengths of man-made genetic material designed to interfere with the production of the protein encoded by the gene. This can shed light on the function of the protein; alternatively, if a disease process results from an excess of certain protein, the method can in theory correct the problem. Faster thantransgenic techniques, but more problematic in practice, antisense has been seen as something of a "black art". There are many technical problems to understand and overcome.