The Ambion® RNA Millennium™ Markers are designed to provide accurate size determination of single-stranded RNA transcripts from 0.5 to 9 kb and can be used in any northern protocol. Sufficient markers are provided for 25 northern gel lanes. They are a mixture of 10 discrete RNA transcripts with easy-to-remember sizes: 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, and 9 kilobases. The markers may be stained with ethidium bromide either during or after electrophoresis. Because of their quantity and even spacing, these markers are ideal for constructing very accurate standard curves for mRNA size determination. They also provide a reference scale for easy verification and comparison of known bands. 1–2 μg (1–2 μg) of RNA Millennium™ Markers will generate 10 distinct bands on a 1% denaturing agarose gel with ethidium bromide staining. All marker lots undergo stringent nuclease testing and are shown to be stable overnight at 37°C.