Changes in the serine/threonine phosphorylation state of a protein in response to various external stimuli can have profound effects on cellular signal transduction, apoptosis and carcinogenesis. The reagents, including phosphorylated protein/peptides, antibodies against the phosphospecific amino acid, are important tools to explore the activation of serine, threonine or tyrosine containing proteins. An aberrant protein phosphorylation is a hallmark of human disease, and the enzymes, particularly protein kinases, which control protein phosphorylation are recognized as a major new drug target family.