In order to study the association of histological grade (HG) with specific clinical and biological parameters which may influence the clinical behavior of infiltrating ductal carcinomas of the breast (IDC), we analyzed in 229 tissue samples the cytosolic concentrations of estrogen receptor (ER), progesterone receptor (PR), pS2, cathepsin D, hyaluronic acid (HA) and tissue-type plasminogen activator (t-PA), as well as those of the erbB2 oncoprotein, epidermal growth factor receptor (EGFR), HA, CD44v5 and CD44v6 in the cell membrane fraction. Likewise, we considered size, ploidy, S-phase fraction and axillary node involvement as variables of the study. The transition from HG1 to HG2 and from HG2 to HG3 was accompanied by a number of common features: global increase in size, greater number of tumors >2.0 cm, decrease in membrane hyaluronic acid concentrations, increased cell proliferation (S-phase >7%) and greater aneuploidy. Other events observed during the transition from HG2 to HG3 were a decrease in ER, PR, t-PA and cytosolic hyaluronic acid. These results led us to consider that HG is associated with certain clinical-biological changes that may help explain its value as a prognostic factor in breast carcinomas.