The history and pulmonary histopathology of 3 siblings, presenting with the association of idiopathic interstitial lung disease, hypocalciuric hypercalcemia, and an intrinsic defect in granulocyte function are described. Prospective examination of 40 family members indicated that the 3 abnormalities are inherited according to an autosomal dominant pattern with, however, a variable penetration. Lung biopsies in the index cases revealed an interstitial infiltration of inflammatory cells and aggregates of conchoid bodies surrounded by multinucleated giant cells. Bronchoalveolar lavage was performed in 11 subjects and often showed an elevated cell recovery and abnormal cell distribution indicative of active alveolitis. In several subjects, multinucleated giant cells were found. The diffusing capacity (in percent predicted) showed a significant decrease with age, independent of smoking habits. The hypocalciuric hypercalcemia was unaffected by steroids or parathyroidectomy. It was not associated with abnormal levels of parathyroid hormone, calcitonin, 25-hydroxy-vitamin D3, 1,25-dihydroxy-vitamin D3, or angiotensin-converting enzyme.