Stromal cell-derived factor-1 (SDF-1) acts as a chemoattractant for leukocytes and can induce neovascularisation. To examine the role of SDF-1 in the development of angiogenesis, immunohistochemical studies were performed on bronchial biopsy specimens from asthmatic and control subjects. Bronchial biopsy specimens were obtained from 13 asthmatic and eight control subjects. The number of vessels and the percentage area they occupied were estimated after staining for type-IV collagen. In addition the number of SDF-1-positive cells was determined. There was a significant increase in the number of vessels and the percentage vascularity in the submucosa of asthmatic subjects compared with control subjects. Asthmatic subjects exhibited a greater number of SDF-1-positive cells in the airway mucosa than control subjects. The degree of vascularity was associated with the number of SDF-1-positive cells. Furthermore, the number of SDF-1-positive cells was inversely correlated with airway calibre and airway hyperresponsiveness. Colocalisation studies revealed that endothelial cells, macrophages and T-lymphocytes were the major sources of SDF-1. These findings suggest that increased vascularity of bronchial mucosa in asthmatic subjects is closely related to the expression of stromal cell-derived factor-1 positive cells, which may play a role in remodelling of airways via angiogenesis.