Some of the most important tools to study p53 protein are various anti-p53 antibodies and immunological methods based on antibody-antigen reactions. Critical comments on the specificity and sensitivity of anti-p53 antibodies have been published. Four monoclonal and two polyclonal anti-p53 antibodies, four of them from two different sources, were compared for their ability to detect in immunoblotting the benzo(a)pyrene-induced p53 from C57BL/6 mouse skin and MCF-7 human breast carcinoma cells. Multiple extra bands were seen with most antibodies. A theoretical comparison of the equivalent epitopes of p53 homologues with the known epitopes of p53 antibodies indicated that the extra bands seen with most antibodies are not due to cross-reactivity with these homologues. A careful adjustment of antibody dilutions is needed for each application utilizing commercial p53 antibodies, regardless of the recommendations of the supplier.