Pulmonary malakoplakia in a patient with the acquired immunodeficiency syndrome. Differential diagnostic considerations. Malakoplakia is an unusual inflammatory condition characterized histopathologically by accumulations of benign macrophages, or von Hansemann's cells, that are associated with diagnostic intracellular and extracellular calcospherites, termed Michaelis-Gutmann bodies. Currently believed to represent an acquired defect of macrophage digestion, malakoplakia most commonly occurs in the urinary tract and is associated with a variety of infectious agents, notably gram-negative bacilli. We describe a patient with the acquired immunodeficiency syndrome who presented with a cavitating lingular mass. A transbronchial biopsy specimen revealed pulmonary malakoplakia, the seventh reported case of this condition and the second reported occurrence of pulmonary malakoplakia in a patient with acquired immunodeficiency syndrome. Microbiological cultures were positive for Rhodococcus equi. The significance of this finding, and the differential diagnosis of intra-alveolar histiocytic proliferations in patients with acquired immunodeficiency syndrome, is discussed. 