TNF is a cytokine recently implicated as an important inflammatory mediator. TNF concentrations in sputa from 13 patients with bronchial asthma on exacerbation and 12 patients with chronic obstructive pulmonary disease were measured. After sonication, the sputa were centrifuged. The supernatants were assayed for the presence of TNF by use of an enzyme-linked immunosorbent assay. TNF was detected in all patients with bronchial asthma (1783 +/- 420 pg/ml), while low values of TNF were detected in only 5 of the 12 COPD patients. It is suggested that TNF is involved in airway inflammation in bronchial asthma.