Neutrophil accumulation in the lower respiratory tract of patients with fibrosing alveolitis is thought to be facilitated by IL-8, a neutrophil chemoattractant primarily secreted by mononuclear phagocytes. The aims of this study were: (i) to explore IL-8 secretion by lung and blood mononuclear phagocytes in subjects with cryptogenic fibrosing alveolitis, systemic sclerosis with and without fibrosing alveolitis, sarcoidosis and normal individuals; (ii) to examine IL-8 secretory heterogeneity in alveolar macrophages and peripheral blood monocytes; and (iii) to correlate alveolar macrophage phenotypic profile to IL-8 secretion. We observed that more monocytes secreted IL-8 than autologous macrophages and that there was heterogeneity in the in vitro IL-8 secretion by alveolar macrophages and peripheral blood monocytes. IL-8 secretion by alveolar macrophages was significantly higher in subjects with fibrosing alveolitis compared with subjects without fibrosing alveolitis, due to a higher percentage of IL-8-secreting alveolar macrophages in the fibrotic group both in the absence (P < 0.002) and presence of lipopolysaccharide (LPS) (P < 0.04) and correlated with bronchoalveolar lavage neutrophil percentage. Using the MoAbs RFD1, RFD7 and RFD9, that distinguish subsets of alveolar macrophages, we have been able to identify associations between secretion of IL-8 and smaller cells and the cells identified by the MoAb RFD7. In situ hybridization of the bronchoalveolar lavage cell population revealed that alveolar macrophages are the predominant source of IL-8 in the lung. We conclude that there is an increased number of IL-8-secreting alveolar macrophages in the lungs of patients with fibrosing alveolitis, and IL-8 secretion by these cells is associated with specific phenotypic profile expression.