The protein encoded by erbB2 oncogene was evaluated by three different methodological approaches (Western blotting, ELISA and immunohistochemistry) in 147 breast cancer specimens. A highly significant correlation was found between Western blotting and ELISA results (p < 0.001). The data from ELISA and Western blotting were categorized as negatives (-), low-overexpressing (+) and high-overexpressing (++). Immunohistochemical results were classified as (-) or (+) according to the absence or the presence of specific staining. Overall positive cases (+ and ++) were 42.2% by Western blotting and 51% by ELISA, while (++) cases were 23.8% and 25.2% respectively. Histochemical staining was found in 29.8% of cases. The two by two evaluation of the assays showed a close association (chi2, p < 0.0001). In particular, the comparison between both ELISA and Western blotting with immunohistochemistry showed concordance rates of 78.9% for ELISA and 83.1% for Western blotting considering the + and ++ cases as a single group. When only the ++ cases were considered as positive, the overall agreement rises to 93.3% and 89.1% respectively. From these preliminary data we conclude that p185 values obtained with the three evaluated methods are possibly superimposable. Nevertheless, the biochemical methods seem to identify an intermediate p185 expression group, whose clinical meaning should be investigated.