Pulmonary alveolar microlithiasis is a rare condition of unknown aetiology which is emerging from obscurity and being more frequently recognized. The case histories of two patients, one of whom is the oldest reported case in the literature, are described. In one case extensive fibrosis of interstitial tissue was present and many calcospherites appeared to lie outside the alveolar spaces. Calcospherites were also found in the bronchial wall of this patient, and this has not previously been reported. The lungs were analysed for calcium, phosphate, and iron, and detailed respiratory function tests were done in one patient; all results were similar to those previously reported in this condition.