Peptide Competition Extracts prepared from HEK 293 cells treated with UV irradiation were resolved on a 10% polyacrylamide gel and transferred to PVDF. Membranes were blocked with a 5% BSATBST buffer overnight at 4oC, then were incubated with p38 [pTpY180/182] antibody for two hours at room temperature in a 3% BSA-TBST buffer, following its prior incubation with: the peptide immunogen (1), a generic phosphothreonine-containing peptide (2), a generic phosphotyrosine-containing peptide (3), the non-phosphorylated peptide corresponding to the phosphopeptide (4), no peptide (5), the phosphopeptide derived from the corresponding region of JNK1&2 (6), and, the phosphopeptide derived from the corresponding region of ERK1&2 (7). After washing, membranes were incubated with goat F(ab’)2 anti-rabbit IgG HRP conjugate and bands were detected using the Pierce SuperSignal method. The data show that only the phosphopeptide corresponding to p38 [pTpY180/182] blocks the antibody signal, thereby demonstrating the specificity of the antibody.