Quantification of growth hormone mRNA in blood

► We describe a sensitive, quantitative assay for growth hormone (GH) mRNA. ► GH mRNA is present in human blood and measurable by the assay in all samples studied. ► The within-person variation of GH mRNA copy number in blood is small. ► GH mRNA copy number in blood is unaffected by acromegaly. ► The tight regulation of GH mRNA copy number in blood remains to be explained.