Hepatic miRNAs regulate developmental changes and contribute to the interindividual variability in the expression of key drug metabolizing enzymes, and thereby, alter drug exposure. This proposals aims at understanding the functional impact of the developmental changes in hepatic miRNA expression on drug metabolism, to identify functional SNPs in miRNA target sites that alter drug metabolism, and to discover plasma miRNA patterns that predict hepatic drug metabolism. This should lead to a better understanding of the role of miRNAs in regulatory mechanisms of the developing liver; ultimately, we expect that it will improve the prediction of variability in drug metabolism across the developmental continuum.