BACKGROUND Heat-shock proteins (hsp) are involved in processes which are associated with tumour neogenesis and the biological behaviour of tumours. The object of our study was to investigate the significance of the 70 kDa hsp for the outcome of women with node-negative breast cancer. PATIENTS AND METHODS Paraffin sections of 191 patients with operated breast cancer and a median follow-up of 177 months were stained immunohistochemically with a commercially available antibody against hsp70. RESULTS We found a statistically significant correlation of the nuclear staining pattern with tumour size (> or < or = 2 cm; p = 0.046) and with a low tumour grading (G1 and G2 versus G3; p = 0.029). Patients showing a cytoplasmatic staining for hsp70 had a statistically significantly decreased overall survival [OS] (p = 0.04) and a shorter survival after recurrence [SR] (p = 0.026). CONCLUSION The nuclear share of hsp70 is associated with various biological characteristics of malignant breast tumours, while the occurrence of cytoplasmatic hsp70 influences OS and SR.