The pleomorphic adenoma gene 1 (PLAG1) is activated by reciprocal chromosomal translocations involving 8q12 in a subset of salivary gland pleomorphic adenomas. PLAG1 encodes a zinc finger protein and was initially reported to be expressed in placenta and fetal tissues, with no detectable expression in other normal adult tissues. By Northern blotting we have detected PLAG1 expression in a wide set of normal adult tissues, including heart, placenta, spleen, prostate, testis, ovary, and small intestine. We have performed reverse transcriptase-PCR and Northern blot analyses to study the expression of PLAG1 in normal salivary gland tissues and in primary cultures and cell lines derived from salivary gland tumors. PLAG1 was expressed in all tumor-derived primary cultures and cell lines, irrespective of their histological type or the presence of genomic rearrangements involving PLAG1, but was not detected by our assays in normal salivary glands. Our data indicate that the presence or absence of PLAG1 expression is not an unequivocal marker for the differential diagnosis of benign versus malignant salivary gland tumors, and that a simple de novo activation of this gene does not fully explain the involvement of this gene in salivary gland tumors.