Seventeen adenoid cystic carcinomas (ACCs) and 27 mucoepidermoid carcinomas (MECs) occurring in the salivary glands were analyzed for p53 tumor suppressor gene alteration (exons 5-8) and protein expression. The cell proliferation activity was also examined by Ki-67 immunohistochemistry. The p53 alterations were detected in three samples (17.6%) of ACC and in four samples (14.8%) of MEC, and were only found in carcinomas arising in the minor salivary glands. The occurrence of the p53 gene alteration is less frequent in ACC and MEC than that in other kinds of tumors, and therefore does not seem to play a critical role in the course of the tumorigenesis in ACC and MEC. All ACC samples arising from the minor salivary glands exhibiting p53 gene alterations showed recurrence/metastasis, thus suggesting a poor outcome of these patients. All ACCs and three out of four MECs samples with p53 gene alterations showed the lowest degree of p53 immunostaining ratio, thus suggesting that no correlation exists between the p53 gene alterations and the p53 immunostaining in these salivary gland carcinomas. No significant relationship was demonstrated between the immunostaining ratio of either p53 or Ki-67 and the morphological growth pattern or patient clinical course in the ACC samples. The p53 immunopositivity in MEC correlated to the histological grade. The Ki-67 immunostaining ratio was also significantly related to the histological grade and the clinical course in MEC.