Anterior pituitary tumors arise sporadically, and also as part of the inherited multiple endocrine neoplasia type 1 (MEN 1) syndrome. To investigate the role of the recently isolated men1 gene in sporadic pituitary tumorigenesis, the complete coding sequence was screened for mutations in 45 sporadic anterior pituitary tumors, including 14 hormone-secreting tumors and 31 nonsecreting tumors, by dideoxy fingerprinting and sequence analysis. No pathogenic sequence changes were found in the men1 coding region. The men1 gene was expressed in 43 of these tumors with sufficient RNA, including one tumor with loss of heterozygosity (LOH) for several polymorphic markers on chromosomal region 11q13. Furthermore, both alleles were expressed in 19 tumors in which the constitutional DNA was heterozygous for intragenic polymorphisms. Thus, inactivation of the men1 tumor suppressor gene, by mutation or by imprinting, does not appear to play a prominent role in sporadic pituitary adenoma pathogenesis.