the subcellular events implicated on the formation and behavior of pituitary adenomas are not fully understood. in this study we investigated the presence of p53, ki-67 and c-erb b2 in 38 pituitary adenomas with immunohistochemical positivity for gh and prolactin (n=26; 68.4%), for prolactin (n=9; 23.7%) and for gh (n=3. 7.8%). the analyses revealed the following results: 24 (63.2%) tumors expressed variable positivity for c-erb b2, 11 (28.9%) expressed p53 positivity and 11 (28.9%) tumors were variably positive for ki-67. our results demonstrated a high percentage of gh/prolactin-, prolactin- and gh-secreting tumors with immunohistochemical positivity for c-erb b2. once this membrane receptor is related to growth factors egf and tgfa and both have a definite effect on tumor growth, our data suggest a possible role for c-erb b2 on the evolution of these tumors.