['The goal of this study was to identify factors that might aid in diagnosis and intraoperative management of hyperparathyroidism.', 'We analyzed biopsy specimens of 242 parathyroids from 159 patients by use of flow cytometry and image cytometry (ICM) for DNA index (DI), defined as the content of nuclear DNA compared with that expected for a DNA diploid standard, for proliferative index (PI), and for ploidy (diploid versus aneuploid or tetraploid).', 'True normal and normal parathyroids from patients with solitary adenomas were uniformly diploid. Abnormal ploidy (aneuploidy or tetraploidy) was identified frequently in adenomas and occasionally in hyperplasias with the exception that multiple endocrine neoplasia (MEN) biopsy specimens were uniformly diploid. DI for adenomas was similar to that for hyperplasias, and DI of both was higher than for normal glands. ICM-DI correlated positively with flow cytometry-DI and patient age and inversely with serum parathyroid hormone. PI was relatively low in all groups but was higher for hyperplasias versus normal parathyroids from patients with solitary adenomas and MEN versus non-MEN. PI correlated inversely with patient age.'] Do dNA index and ploidy distinguish normal human parathyroids from parathyroid adenomas and primary hyperplastic parathyroids?