Considerable attention has been given to the accuracy of HER-2 testing and the correlation between the resultsof different testing methods. This interest reflects the growing importance of HER-2 status in the managementof patients with breast cancer. In this study the detection of HER-2 gene and centromere 17 status was evaluatedusing dual-colour primed in situ labelling (PRINS) in comparison with fluorescence in situ hybridization (FISH).These two methods were evaluated on a series of 27 formalin fixed paraffin embedded breast carcinoma tumours,previously tested for protein overexpression by HercepTest (grouped into Hercep 1+/0, 2+ and 3+). HER-2 geneamplification (ratio≥2.2) by PRINS was found in 3:3, 6:21 and 0:3 in IHC 3+, 2+ and 1+/0 cases, respectively.Comparing FISH and IHC (immunohistochemistry), showed the same results as for PRINS and IHC. Chromosome17 aneusomy was found in 10 of 21 IHC 2+ cases (47.6%), of which 1 (10%) showed hypodisomy (chromosome17 copy number per cell≤1.75), 7 (70%) showed low polysomy (chromosome 17 copy number per cell=2.26 - 3.75)and 2 (20%) showed high polysomy (chromosome 17 copy number per cell ≥3.76). The overall concordance ofdetection of HER-2 gene amplification by FISH and PRINS was 100% (27:27). Furthermore, both the level ofHER-2 amplification and copy number of CEN17 analysis results correlated well between the two methods. Inconclusion, PRINS is a reliable, reproducible technique and in our opinion can be used as an additional test todetermine HER-2 status in breast tumours.