"It is tempting to propose that careful screening of patients with peptic ulcer for hyperparathyroidism would yield cases of hyperparathyroidism which are not being recognized at present." With these words Marden Black in his monograph1remarked the unusual frequency with which peptic ulcer disease is encountered among patients exhibiting hyperparathyroidism.2Clinical evidence compels one to consider that this frequency may be greater than that expected by chance alone.3Laboratory data suggest that a real, although undefined, influence is exerted by parathyroid hormone on gastric acid secretion4and on the gastrointestinal mucosa.5Although Culver and St. Goar6(and later Black himself7) have doubted the justifiable yield of surveying peptic ulcer patients for hyperparathyroidism, it occurred to us that the fertility of the field should be tested. The purpose of this paper is to report the results of such a survey and to comment on the difficulties encountered in studying