Western blot is often used in research to separate and identify proteins. One simple and common use for Western blotting is to identify whether a particular protein is present or absent in a sample by looking for a band of the correct size on a Western blot . This routine type of Western blot is used to either test for endogenous cellular expression of a target protein, or to examine transfected cell lines to see if expression has been conferred by the introduction of a DNA construct . It is also used with techniques such as protein purification and cellular fractionation to identify which samples have the target protein, and thus is an aid to deciding which samples to combine or discard .

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In this technique a mixture of proteins is separated based on molecular weight, and thus by type, through gel electrophoresis. These results are then transferred to a membrane producing a band for each protein. The membrane is then incubated with labels antibodies specific to the protein of interest. The unbound antibody is washed off leaving only the bound antibody to the protein of interest. The bound antibodies are then detected by developing the film. As the antibodies only bind to the protein of interest, only one band should be visible. The thickness of the band corresponds to the amount of protein present; thus doing a standard can indicate the amount of protein present.