We examined the effects of estrogen on tumor necrosis factor α (TNF- α)-induced expression of intracellular adhesion molecule (ICAM-1) and vascular adhesion molecule (VCAM-1) in cultured human bronchial smooth muscle cells (BSMC). Experiments were performed in triplicate in T-75 tissue culture flasks containing normal human BSMC. Four experiments were carried out: untreated BSMC cells (control); TNF-α 1000 U/ml stimulation of BSMC; forskolin 5 μM before TNF-α stimulation of BSMC; and estradiol 30 μM before TNF-α stimulation of BSMC. Cyclic adenosine monophosphate was measured by a commercially available radioimmunoassay kit. Cell expression of ICAM-1 and VCAM-1 was quantified by flow cytometry. Incubation of cells with TNF-α 1000 U/ml for 24 hours elicited a 27-fold increase in basal expression of ICAM-1 and a 2-fold increase in VCAM-1 (p>0.05). Incubation of BSMC with forskolin 5 μM, for 1 hour before TNF-α, decreased TNF-α-induced expression of ICAM-1 by 62% and VCAM-1 slightly by 17%. The BSMC incubated with estradiol 30 μM, 1 hour before TNF-α, decreased TNFα-induced expression of ICAM-1 by 21%; VCAM-1 remained unchanged (p>0.05). We found a trend toward inhibition of TNF-α-stimulated ICAM-1 expression in cultured BSMC with pretreatment with estradiol. However, due to large variability within the cell culture model, statistical significance was not reached.