Northern blot is essentially a combination of denaturing RNA gel electrophoresis and a blot to a support membrane. In this Northern blot process, RNA is separated based on size and is then transferred to a membrane that is then probed with a labeled complementary sequence. The results are visualized, depending on the label used; however, most result in various RNA bands representing the sizes of the RNA detected in the sample. The intensity of these bands is related to the amount of the target RNA in the samples analyzed. This procedure is commonly used by MarinBio and others to monitor when and how much gene expression is occurring by measuring how much of that RNA is present in different samples. Northern blotting is a common technique for determining at what time, and under what conditions, certain genes are expressed in living cells and the effects of drugs on RNA expression.