Evaluation of gene amplification and protein expression of the c-erbB-2/neu in breast carcinomas has been an important task in breast cancer management. Although immunohistochemistry is widely applied, fluorescence in situ hybridization (FISH) technology shows its advantage in discriminating tumors in an objective manner. More recently, development of LightCycler technology permits evaluation of gene amplification with a small volume of DNA run in a 20 microL glass capillary. In this study, a series of 87 breast carcinomas were chosen for evaluation of c-erbB-2/neu gene amplification detected by both LightCycler technology and FISH. Real-time polymerase chain reaction (PCR) was performed in LightCycler capillaries with 10 ng sample DNA. By using LightCycler Relative Quantification Software version 1 (LightCycler, Roche, Mannheim, Germany), the amount of c-erbB-2 DNA was calculated as a ratio of c-erbB-2/reference gene quantity in a sample, and then the ratio was divided by the ratio of c-erbB-2 gene/reference gene quantities of a calibrator DNA (a standard DNA provided in the kit), which was run with each sample reaction in parallel. Dual-color FISH was performed on sections of the formalin-fixed, paraffin-embedded tissue array samples using the DAKO HER2 FISH pharmDX kit (DAKO A/S, Glostrup, Danmark) according to the manufacturer's instructions. Furthermore, immunohistochemistry was performed in parallel, with both the NCL-CB11 and HercepTest antibodies. Both the FISH technology and the LightCycler-PCR identified a similar percentage of tumors with c-erbB-2 gene amplification in our present study, 16% (14/87) and 15% (13/87), respectively, whereas immunohistochemistry demonstrated 32% and 34% c-erbB-2 overexpression with the NCL-CB11 and HercepTest antibodies, respectively. In addition, FISH and PCR were highly correlated in detecting tumors mainly with 3+++ c-erbB-2 protein expression by immunohistochemistry, indicating that LightCycler real-time quantification of c-erbB-2 gene may be an alternative to FISH in breast cancer clinical application.