10.22376/ijpbs.2019.10.1.p1-12 Volume 2 Issue 4 2011 (October - December) Even today, new drugs are usually not discovered by rational drug design although this would be the dream of the medically oriented chemist. On an average, it is still necessary to synthesize and test about 10000 new compounds in order to discover a new active substance. In many cases, the active substance is to be directed against proteins such as enzymes, receptors, or ion channels, the structure and mode of action of which are usually very complicated and often incompletely understood. Over past two decades, the use of nucleic acid – based inhibitors of gene expression (antisense agents) has come in and out of fashion. Deep in a patient's genome lies a malfunctioning span of genetic code. If its chemical complement were constructed - a strand of nucleic acid carrying, for instance, the code letter T where the malfunction has an A, and a G where the malfunction has a C and if the strand entered cells and encountered the code, it binds specifically there, by the same interactions - T with A, G with C - responsible for assembling a normal DNA double helix. The resulting hybrid jams the malfunction, preventing it from being expressed as a disease. So, the short spans of "antisense" will be genetic therapy for various diseases such as viral pathogens (Human Immunodeficiency Virus lessThan i greaterThan in vitro lessThan /i greaterThan and cytomegalovirus lessThan i greaterThan in vivo lessThan /i greaterThan ), and variety of hematologic malignancies. Today, it continues to be the basis for seeking a new, genetic kind of magic bullet. S. D. Sawant, G. N. Patil, B. T. Tare And A. V. Patwa Antisense oligonucleotides, DNAzymes, Peptide Nucleic Acid and Ribozyme. 140-155