MoAbF9 immunoreactivity was investigated in frozen sections of 123 breast carcinomas using an avidin or streptavidin biotin peroxidase kit. A standardized computer image analysis system was used to evaluate immunostaining. The percent of cell surface staining and mean optical densities were correlated with morphological criteria of prognosis such as tumor size histological grade, blood and lymph invasion and axillary lymph node involvement, with immunoreactivity to other MoAb, i.e. Ki67, anti-RE and anti-RP, anti-p.HER-2/neu and with tumor aneuploidy and AgNORs content in tumor cell nuclei. Despite some heterogeneity, MoAbF9 was reactive with all breast carcinomas tested. The percent of F9 immunostained cell surface and mean optical density increased with Ki67 immunoreactivity, tumor aneuploidy and AgNORs nucleus surface but were independent of p.HER-2/neu oncoprotein distribution and tumor receptor content. These findings suggest that F9 could not only allow detection axillary lymph node micrometastases but also be used as plasmatic marker for tumor recurrence and metastases.