The DNA content of ductal breast carcinomas of varying histological grade was measured using static image cytometry and correlated with pS2 expression in the tumour cells. Our study was performed on imprint of surgical biopsies of 60 women with ductal breast cancer. A statistically significant difference was observed between pS2+ expression and grade of malignancy (P < 0.001). The percentage of euploid tumours significantly decreased from grade I to grade II to grade III (P = 0.01). The percentage of aneuploid tumours increased from pS2+ to pS2- breast tumours (P < 0.001). These findings may be indicative of pS2 and DNA ploidy alterations and tumour aggressiveness.