To examine SteC-dependent phosphorylation of MEK during bacterial infection, we infected Swiss 3T3 fibroblasts with different strains of S. Typhimurium for 8 hr and subjected lysates to immunoblotting with an antibody recognizing MEK1 and MEK2 phosphorylated on the two activatory residues: S218 and S222. This evidence concerns the gene MAP2K1 and bacterial infectious disease.