Twenty burned patients divided in three groups according to the severity of the lesions were investigated at 1- or 2-day intervals for up to 5 weeks after injury. Plasma elastase levels were elevated during the first day after injury and were correlated with the area of the burns. However, plasma elastase was rapidly bound and inactivated by protease inhibitors. Leucocyte counts, fever and the concentration of alpha-1-proteinase inhibitor were not correlated with the extent of the burn. The rise of plasma elastase was not accompanied by consumption of the elastase inhibitory capacity (EIC) of plasma, which increased to a plateau around day 5. The EIC values were in accord with the rise of alpha-1-proteinase inhibitor, the major anti-elastase agent in plasma. Studies of blister fluid in eight patients showed that the elastase content was higher than that of corresponding plasma, while the concentration of alpha 1-proteinase inhibitor and the EIC were comparable with those of plasma. Measurements of the levels of tumour necrosis factor released by stimulated macrophages in five patients with major burns showed no significant increase compared with controls.