Total cell Iysates are useful as both positive and negative controls in immunoblotting. A431, a human epidermoid carcinoma cell line, and the EGF-stimulated A431 Iysates are used as negative and positive controls, respectively, when studying the phosphorylation cascade initiated by ligand binding to receptor tyrosine kinases. Both A431 and normal human fibroblasts are valuable positive controls for antibodies to proteins expressed in these cells. The mouse fibroblast cell line 3T3 and its RSV-tr