Thirty patients known to have or suspected of having acquired immunodeficiency syndrome (AIDS) were evaluated for opportunistic pulmonary infection using a double lumen lavage catheter (DLL). Lavage specimens obtained were cytocentrifuged and initially stained by the Papanicolaou technique as a means of rapid evaluation for Pneumocystis carinii. If no opportunistic organism was identified, the patient underwent further diagnostic investigations. In 18 patients receiving mechanical ventilatory support, the procedure was performed via the endotracheal tube. Twelve patients who were less severely ill underwent the procedure via the transnasal route. In 43 percent (13/30), opportunistic infections were diagnosed by DLL. Twelve had P carinii, one of whom had cytomegalovirus and another of whom had Herpes simplex viruses, and one with Toxoplasma gondii. Thus, the sensitivity for all opportunistic infections was 86 percent (12/14). The volume of fluid recovered averaged 93 percent of that instilled. There was no significant difference between prelavage and postlavage PaO2. In this group of patients, double lumen lavage obviated the need for more invasive and expensive procedures.