Three patients with leucocyte related immune deficiency developed pneumatoceles during acute bacterial pneumonia. A fourth patient with chronic granulomatous disease of childhood developed persistent lung cysts following pulmonary abscesses. The pneumatoceles persisted without significant change for one year to five years. In 25 immunologically normal patients, pneumatoceles that were associated with acute bacterial pneumonia resolved in 3 weeks to 11 months. Perhaps alterations in leukocytic function and in local inflammatory response result in fibrotic cellular reaction and sequestration of parenchymal air collections, precluding their resorption.