Ethidium bromide fluorescence of 28S ribosomal RNA can be used to normalize samples in northern or dot blots when analyzing small drug-induced changes in specific mRNA.

Quantitative analysis of Northern blots is frequently accomplished with the aid of an internal standard. Most common is probing for an additional message the steady-state levels of which do not change in response to the experimental conditions and the signal of which is sufficiently removed from that of the target gene after gel electrophoresis. However, this strategy is not always feasible. When total RNA is immobilized on nylon, 28S ribosomal RNA on the blot can be used as an internal standard and quantitated by scanning the negative photograph of the blotted RNA stained with ethidium bromide. This procedure can also be used for RNA dot blots. The method is quick, reliable, will work with laser or white-light densitometers, and can serve as a universal internal standard, eliminating the need for additional probes.