Primary tumours from 100 Norwegian node-negative breast carcinoma patients were examined for c-erbB-2, int-2, and c-myc proto-oncogene amplification. c-erbB-2, int-2, and c-myc amplification was found in 12.1% (12 of 99), 8.6% (8 of 93), and 1.1% (1 of 89) of the samples respectively. All the c-erbB-2 amplified tumours were of the ductal type, and all the int-2 amplified tumours were oestrogen receptor positive. No other significant or borderline significant associations between gene amplification and clinical or histopathological parameters were found. Relapse occurred more frequently in patients with c-erbB-2 gene amplification (relapse in 33.3% of the patients with c-erbB-2 amplification compared to 20.7% in the non-amplified group), but the difference was not statistically significant, int-2 amplification was not associated with increased risk of relapse, whereas the prognostic value of the c-myc amplification could not be evaluated.