Detection of phosphorylation by western blotting is an important procedure to elucidate molecular mechanisms in signal transduction pathways involving kinases and phosphatases. Anti-phospho-tyrosine monoclonal antibodies have been widely used because they react with plethora of proteins containing phosphorylated tyrosine residues. In contrast, the monoclonal antibodies against phospho-serine or threonine residues are unpopular, since their affinity and specificity are less than optimal. To achieve precise characterization of signaling events, it is desirable to raise a good anti-phospho-site-specific antibody to clearly detect phosphorylated species. However, raising this type of antibody is costly and time-consuming, and sometimes results in failure.