In order to obtain prognostic clinicopathological information, 49 cases of pure ductal carcinoma in situ of the breast (DCIS), were evaluated for the immunohistochemical expression of potential predictor markers including c-erbB-2 oncogene product, p53 protein, oestrogen (ER) and progesterone (PR) receptors, oestrogen-regulated proteins pS2 and cathepsin-D (cath-D), CD44 protein and 67-kDa laminin receptor (MLuC5). Immunohistochemical findings were compared with conventional pathological parameters, clinical findings, and the clinical outcome of the patients. When markers were matched to each other, statistical analyses provided a significant positive correlation between c-erbB-2 overexpression and p53 positivity (P < 0.01) and between ER and PR (P < 0.01), ER, PR and pS2 (P < 0.01), pS2 and MLuC5 (P < 0.05). Significant negative correlations between c-erbB-2 overexpression and ER (P < 0.05), PR (P < 0.01) and pS2 (P < 0.01) positivity was also observed. Data on the relationship between marker status and pathological findings revealed a significant positive trend between c-erbB-2, p53, and increased grade values (P < 0.05) and opposite results with PR receptor expression (P < 0.01). c-erbB-2 overexpression was further significantly associated with comedotype carcinoma (P < 0.05) and distribution of disease in confluent neoplastic ducts (P < 0.01). Although no statistically significant correlation among biological markers expression, clinical findings and outcome was demonstrated, overall this study indicates that tumour cells from a subset of DCIS, which includes comedotype carcinoma, express significantly unfavourable prognostic factors.