Carbon-laden macrophages in bronchoalveolar lavage have been noted to be associated with a history of crack smoking. We report herein the finding of carbon-laden macrophages in four cytological preparations of pleural fluid from two crack smokers. The etiology of the two patients' pleural effusions differed; neither had a bronchopleural fistula. Patient 1 had AIDS, Pneumocystis carinii pneumonia, and Kaposi's sarcoma of the right lung with an associated bilateral pleural effusion. Patient 2 was HIV seropositive, had pulmonary tuberculosis, hepatitis A, B, and C, cardiomyopathy, pulmonary embolism, and bilateral pleural effusions, the latter of which were probably due to cardio-pulmonary dysfunction. An additional two crack smokers with pleural effusions due to malignancy, one primary pulmonary adenocarcinoma and the other metastatic melanoma, did not have carbon-like material in their pleural fluid cytology. We hypothesize that intracellular accumulation of carbonaceous material in the lung parenchyma and pleural space occurs when normal clearance mechanisms are overwhelmed.