Authors investigated the expression of proliferationg cell nuclear antigen(PCNA) and the numbers of nucleolar arganizer region(NOR) in breast carcinomas correlation with tumor grade. The specimens used in this study were 14 cases of invasive ductal carciomas, 3 cases of invasive carcinomas with predominent intraductal component, 1 case of mucinous carcinoma, 2 cases of invasive papillary carcinomas and 1 case of medullary carcinoma. All cases were graded using modified grading system according to Bloom and Richardson. The grade I, II and III were 7 cases, respectively. PCNA was recognized immunohistochemically in paraffin sections by the monoclonal antibody PC-l0. On the other hand, NOR was demonstrated in paraffin sections using argyrophillic mehod(AgNOR). The present study showed a significant correlation of PCNA index and of AgNOR number with the histological grade(PCNA: I vs II, P<0.05; II vs III, p<0.05 and AgNOR: I vs II, p>0.05; II vs III, p >0.05; I vs III, p<0.05). The overall expression of PCNA was significantly correlated with AgNOR number(Spearman r=0.624, p<0.05). On the basis of above findings it wss considered that degree of the expression of PCNA and mean AgNOR number may be successefully applied as routine makers to the assessment of the growth potential of breast carcinomas.