The purpose of Applications Therapeutic of Ribozymes is to provide an overview of the utility of ribozymes to selectively inhibit the expression of RNA. The ribozyme applications appearing in this book should benefit not only those experienced in ribozymes, but also those applying this ribozyme technology for the first time. It is hoped that a better understanding of the therapeutic application ofribozymes will have a significant impact on human disease in the near future. The field ofribozyme biochemistry has come a long way since the initial observation that RNA is capable of catalysis, initially in cis during processing of larger molecules and ultimately the use of ribozymes in trans to achieve cleavage of target sequence. The fundamental observation that hammerhead (and subsequently hairpin) ribozymes could be designed to cleave a target messenger RNA, and the clarification of sequence restrictions in both the ribozyme and the target RNA, have paved the ways for the use of ribozymes as a tool to manipulate gene expression at the molecular level. This had pre- ously been a domain of antisense oligonucleotides and triplex DNA. Sub- quent studies have explored the myriad biological systems in which ribozyme-mediated inhibition of genes involved in various cellular processes may be used to uncouple important signaling pathways or to reverse the p- notypic expression of a pathologic process.