We investigated the in vitro candidacidal activity of alveolar macrophages (AM) and peripheral blood monocytes (PBM) from normal subjects or from patients with chronic obstructive pulmonary disease (COPD) displaying defective skin test delayed-type hypersensitivity (DTH) reactivity to seven antigens including Candida albicans. The results showed that cells from patients with COPD were significantly less effective than cells from control subjects in the killing of C. albicans. To explore whether the observed functional impairment could be reversed, interferon-gamma (IFN-gamma) was added to AM and PBM from patients with COPD, alone or in the presence of lipopolysaccharide (LPS) as a suboptimal stimulus. The cells were cultured for 24 h and then assayed for anti-Candida activity. After IFN-gamma treatment, the fungicidal activity of cells from patients with COPD was comparable to that of unstimulated AM or PBM from healthy donors. Treatment with IFN-gamma plus LPS resulted in a further enhancement in the killing of C. albicans. To gain more insight into the mechanisms involved in the modulation of killing, we evaluated the possible stimulating activity of IFN-gamma plus LPS treatment on the secretion of tumor necrosis factor (TNF) and interleukin-1 (IL-1), two cytokines produced by activated macrophages and capable of stimulating natural effectors. The results showed that IFN-gamma plus LPS can indeed stimulate TNF and IL-1 secretion by AM and PBM from patients with COPD. Therefore, a precise role can reasonably be ascribed to these soluble factors in the observed augmentation of candidacidal activity as ascertained by treatment with IFN-gamma plus LPS.