Objective: Sulfur mustard (SM), a chemical warfare agent, interferes with fundamental cellular processes such as DNA replication, transcription and translation. It also affects divergent cellular responses/pathways including cell cycle control, apoptosis/necrosis, electron transport, cell adhesion, inflammatory response, and morphogenesis and repair. However, its affects on human cells and tissues are poorly understood. MicroRNAs (miRNAs) are a novel post-transcriptional gene regulators, each targeting several (even >100) mRNAs. They are being indicated in an increasing number of cellular abnormalities, so holding promise as possible therapeutics or therapeutic targets through the use of miRNA mimics or antagomirs, respectively. However, to date, the role of miRNAs in the cellular response to sulfur mustard has remained entirely unnoticed. Aberrant expression of miR-21 and miR17-92 has been associated with various cellular abnormalities. These miRNAs are validated to control targets in P53, NFkB, apoptosis, JAK-STAT, TGF-β and AKT pathways. As these pathways are already shown to - through microarray studies- contribute to SM pathogenesis, it would be interesting to assess the effects of SM exposure on these miRNAs. Materials and Methods: Normal human fibroblasts were maintained in RPMI (37°C, 5% CO2). Near-confluent cell cultures were exposed to 50, 150, and 300 micromoles of SM for different time pointss (.5, 1, 10 hrs) and were used along with skin biopsies obtained from Iranian veterans to determine changes in mir-21 and mir-17-92 cluster. After RNA extraction and cDNA synthesis the expression of candidate miRNAs were assayed using real time PCR. Results: Using LNA specific primers, we were able to detect and quantify the expression of mir-21 and mir-20a in exposed cells, and skin biopsies. Our preliminary data suggest that mir-21 and mir-20a are downregulated in biopsies obtained from lesion areas of skin, in comparison to the normal skin tissue from the same patient. SM exposure on fibroblast cells also altered the expression of mir-21 and mir-20a, in a dose-dependent manner Conclusion: Our data suggest that SM exposure could cause expression alteration in miRNAs, and that this alteration might contribute to the pathogenesis of the exposed tissues.