The large body of work on miRNA and mRNA in diagnostics may be surprising since these molecules are much more susceptible to nuclease degradation than DNA. However, the essential roles of mRNA and miRNA in cellular metabolism make them excellent biomarkers for the study of normal cellular processes and the diagnosis of disease. Metabolic diseases such as cancer as well as infectious diseases can be diagnosed via miRNA biomarkers by reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR) and lateral flow immunoassays. High-throughput sequencing of total cellular mRNA pinpoints changes in gene expression that can be used in diagnosis. The specificity of the CRISPR system for its target DNA makes it a potential tool with both diagnostic and therapeutic purposes. The number of journal publications and patents using RNA for diagnosis demonstrates its power (Figure ); however, a comprehensive review of RNA as a diagnostic biomarker or, in the case of CRISPR RNA, as a diagnostic agent, is beyond the scope of this review. Here we focus on RNAs as therapeutic agents.