We analyzed genomic DNA from 43 sporadic benign parathyroid adenomas for rearrangements of the PTH gene, and for point mutations of the H-ras (codons 12, 13, and 61), N-ras (codons 12, 13, and 61), and K-ras (codons 12 and 13) genes. One of 43 parathyroid adenomas showed a chromosome 11 rearrangement involving both the PTH gene on the short arm of chromosome 11 (at band p15) and a locus on the long arm (11q13). This rearrangement was indistinguishable from one that was previously described in a parathyroid adenoma by Arnold et al., indicating that this may be an important contributor to tumorigenesis in a small subset of patients with parathyroid adenoma. H-ras, K-ras, and N-ras oncogene activation by point mutation at codons 12, 13, or 61, known to occur in many tumors, could not be detected in any parathyroid adenoma.