THE AIM of our study was to evaluate the prognostic significance of p53 protein immunoreactivity for prostate cancer and to determine whether p53 immunoreactivity correlates with the Gleason tumor grade in primary adenocarcinoma. Prostate fragments were fixed in 10% formalin, paraffin-embedded, sectioned and standard Hematoxylin-Eosin stained, then examined using histological grade (Gleason system). P53 expression was studied using immunohistochemistry with monoclonal antibody anti-p53, 1 : 100 (BIOX) on tissue samples obtained during transurethral electroresection, adenomectomy or needle biopsy in 30 patients with prostate carcinoma: group 1 (n = 7) Gleason score 5, group 2 (n = 10) Gleason score 6, group 3 (n = 11) Gleason score 7, group 4 (n = 2) Gleason score 8. Also, we noted the cases with high grade prostatic intraepithelial neoplasia (high grade PIN). All specimens prior to initiation of any treatment were submitted for this study. Staining was defined as positive for p53 whenever any specific nuclear staining was detected. We considered tumors to overexpress p53 protein only when strong nuclear staining was present. Cases exhibiting weak or equivocal nuclear staining were classified as negative, as were cases with extremely rare isolated positive nuclei. A semiquantitative scoring system was employed to assess the level of p53 reactivity. Six of 17 (35.2%) moderately differentiated tumors (Gleason score 5-6) and five of 13 (38.4%) moderate to poorly differentiated (Gleason score 7 and above) revealed strong nuclear positivity for p53. In addition, we noted occasional p53 reactivity in high-grade PIN.We interpret these data to demonstrate a positive association between p53 reactivity and higher Gleason grade tumors; p53 might be an independent prognostic indicator among metastatic risk cases.