MicroRNAs (miRNAs) are small non-coding RNA molecules that have recently been discovered to regulate gene expression. The regulatory effects of these molecules on genes involved in tumor formation present exciting possibilities for anti-cancer therapy. In human NT2 teratocarcinoma cells, the RE1 Silencing Transcription Factor (REST) is important in regulating cellular differentiation into neurons and possibly proliferation into cancer tumors. Data from target validation experiments suggests that mir-26a and mir-17-5p may downregulate REST expression in NT2 cells by repressing translation. Western and Polymerase Chain Reaction (PCR) analysis indicates that mir-302b may indirectly upregulate REST expression by repressing a transcription factor involved in the synthesis of REST mRNA. Data from Northern hybridization reveals that the addition of anti-sense miRNA oligomers can downregulate cellular expression of miRNA whereas addition of pre-cursor miRNA upregulates the endogenous levels of miRNA. Manipulating the expression of these regulatory molecules allows for control of important genes involved in cancer pathways or the pathways of other human diseases. As these cellular effects are further understood, miRNAs are likely to play an important role in developing disease therapies based on gene regulation.