Expression quantitative trait loci (eQTLs) are genetic variants associated with variation in steady-state gene expression levels. Now, Athma Pai, Jonathan Pritchard, Yoav Gilad and colleagues report a study that identifies QTLs associated with mRNA decay rates (PLoS Genet. 8, e1003000, 2012). The authors determine the gene expression decay rates of over 16,000 genes in 70 human lymphoblastoid cell lines from the HapMap Project for which there is whole-genome genotype data available. To measure decay rates, they treated cells with an RNA elongation complex inhibitor, actinomycin D, and measured changes in mRNA abundance at various time points after treatment. They observed both variation in decay rates between genes and variation in decay rates between individuals within the same gene. They mapped genetic variation associated with the quantitative trait of mRNA decay rate and found 195 loci, called RNA decay QTLs (rdQTLs). The authors estimate that the expression of 10% of genes is influenced by variation in decay rates and that mRNA decay rates contribute to the mechanism of a substantial fraction of eQTLs.