The clinical features of PCP differ according to the factors responsible for the predisposing immunosuppression. Although the diagnosis of PCP often requires BAL, the profiles of the inflammatory mediators in the BAL fluid are not thoroughly documented. The aim of the current study was to characterize the profiles of inflammatory mediators in BAL fluid during PCP in patients with underlying autoimmune diseases, malignancies, or AIDS. The medical records of 14 patients with autoimmune diseases, 10 with malignancies, and 8 with AIDS, all of whom had been diagnosed with PCP by microscopic examination of BAL fluid, were reviewed. The concentrations of TNF-alpha, MCP-1, HMGB1, IL-8, IL-6, IL-10, and IFN-gamma in the BAL fluid that had been obtained for the diagnosis of PCP were measured. The concentrations of MCP-1, IL-8, and IL-6 differed according to the underlying disease, tending to be higher in patients with autoimmune diseases and lower in those with AIDS. The concentrations of HMGB1, IL-8, and IL-6 were positively correlated with the proportion of neutrophils in BAL fluid and inversely with the oxygenation index. Although the serum concentrations of CRP and LDH were positively correlated with those of IL-8 and MCP-1, none of the mediators in BAL fluid was correlated with the serum beta-D-glucan concentration. The production of inflammatory mediators in the lung differed between the patient groups with different underlying disorders. The modest upregulation of IL-8 and IL-6 might be associated with the milder clinical manifestations of PCP in AIDS patients.