In 10 patients who received a heart lung transplant, TNF-alpha generation by cells collected during bronchioloalveolar lavages (n = 30) and by circulating mononuclear cells was measured. Basal and recombinant IL-2-stimulated productions (50 U/ml) were measured. TNF-alpha concentration was determined by an immunoradiometric assay (IRMA). Circulating mononuclear cells produced at least 4 times less TNF-alpha than BAL cells. Rejection episodes or CMV diseases were not associated with significant changes in TNF-alpha generation. Recombinant IL-2 increased this production in both cell populations but the magnitude of this effect was smaller in BAL cells, suggesting an in vivo preactivation.