Several chronic diseases are characterized by inflammation, T cell recruitment and tissue remodelling. We hypothesized that activated T cells may stimulate remodelling of extracellular matrix (ECM) in vitro. Total T cells (CD3+) as well as CD4+ and CD8+ subsets were isolated from peripheral blood and stimulated, after which conditioned media (CM) were obtained. CM was added to human lung fibroblasts in three-dimensional collagen gels and the area of gels was measured daily. Hydroxyproline was determined as a measure of collagen degradation in the gels. Matrix metalloproteinase (MMP) activity in the culture media was analysed by gelatine zymography. Cytokine secretion of stimulated CD4+ and CD8+ T cells was analysed. CD3+ CM augmented collagen gel contraction in a time- and dose-dependent manner (P < 0.0001). CD4+ T cell CM was more potent than CD8+ T cell CM (P < 0.001). CD3+ CM and CD4+ T cell CM, but not CD8+ T cell CM, stimulated fibroblast-mediated collagen degradation and MMP-9 activity. A broad-spectrum MMP-inhibitor added to the culture system inhibited both gel contraction and MMP activity. Activated CD4+ T cells secreted significantly more tumour necrosis factor (TNF) and interleukin (IL)-6 compared to CD8+ T cells. CD3+ CM from patients with chronic obstructive pulmonary disease stimulated fibroblast-mediated collagen gel contraction to the same magnitude as CD3+ CM from healthy controls. In conclusion, activated CD4+ T cells can stimulate fibroblast-mediated degradation of ECM in vitro. This could be a mechanism by which activated T cells stimulate degradation of lung tissue leading to pulmonary emphysema.