This study identifies and defines miRNA expression in circulating plasma microvesicles of normal subjects. Microvesicles, also known as exosomes or microparticles, circulate in the peripheral blood and can stimulate cellular signaling. The researchers hypothesized that under normal healthy conditions, microvesicles contain miRNAs, contributing to biological homeostasis. Microvesicles were isolated from the plasma of normal healthy individuals, and RNA was extracted from both the microvesicles and matched mononuclear cells. The RNA was profiled for 420 known mature miRNAs by real-time PCR. Hierarchical clustering of the data sets indicated significant differences in miRNA expression between peripheral blood mononuclear cells (PBMC) and plasma microvesicles. The study found 71 miRNAs co-expressed between microvesicles and PBMC, with 33 and 4 significantly differentially expressed miRNAs in the plasma microvesicles and mononuclear cells, respectively. The majority of the miRNAs expressed in the microvesicles were predicted to regulate cellular differentiation of blood cells and metabolic pathways. The study also found that a select few miRNAs were predicted to be important modulators of immune function. The data generated from this study provides a basis for future studies to determine the predictive role of peripheral blood miRNA signatures in human disease and will enable the definition of the biological processes regulated by these miRNAs. The study is the first to identify and define miRNA expression in circulating plasma microvesicles of normal subjects.This study identifies and defines miRNA expression in circulating plasma microvesicles of normal subjects. Microvesicles, also known as exosomes or microparticles, circulate in the peripheral blood and can stimulate cellular signaling. The researchers hypothesized that under normal healthy conditions, microvesicles contain miRNAs, contributing to biological homeostasis. Microvesicles were isolated from the plasma of normal healthy individuals, and RNA was extracted from both the microvesicles and matched mononuclear cells. The RNA was profiled for 420 known mature miRNAs by real-time PCR. Hierarchical clustering of the data sets indicated significant differences in miRNA expression between peripheral blood mononuclear cells (PBMC) and plasma microvesicles. The study found 71 miRNAs co-expressed between microvesicles and PBMC, with 33 and 4 significantly differentially expressed miRNAs in the plasma microvesicles and mononuclear cells, respectively. The majority of the miRNAs expressed in the microvesicles were predicted to regulate cellular differentiation of blood cells and metabolic pathways. The study also found that a select few miRNAs were predicted to be important modulators of immune function. The data generated from this study provides a basis for future studies to determine the predictive role of peripheral blood miRNA signatures in human disease and will enable the definition of the biological processes regulated by these miRNAs. The study is the first to identify and define miRNA expression in circulating plasma microvesicles of normal subjects.