Overexpression of Her-2/neu-oncoprotein is used as marker for Herceptin therapy. To investigate the sensitivity and specificity of automatic immunohistochemistry (Benchmark, Ventana), we compared the results to the manual testing (Dako) in 130 breast carcinomas and validated the results by fluorescence in situ hybridization (FISH). Manual and automatic immunohistochemistry of Her-2/neu-oncoprotein using two different antibodies (HercepTest, Her-2/neuTest 4B5) was analyzed. FISH was performed in all cases with uncertain or strong overexpression in either immunohistochemical stainings or with different immunohistochemical results. Same immunohistochemical results were seen in 73.8%. Two cases with overexpression, detected with Her-2/neuTest 4B5 and confirmed by FISH, showed no overexpression using HercepTest. From 21 cases with 2+ by Her-2/neuTest 4B5, 15 cases had no gene amplification (two of them with 3+ HercepTest); three cases showed a gene amplification (one of them with failing overexpression by HercepTest); two other cases were polysomic; one could not be analyzed. Ventana immunohistochemistry seems to be of same reliability like Dako with a little better concordance to FISH in our study.