The different roles of bronchial and pulmonary circulation in the tracheal blood supply were investigated in 26 female rats: a control group (CG, n = 7), a group with pulmonary hilar ligation (PL, n = 5), another with tracheal transsection (TL, n = 9) and a group with both these procedures (TL&PL, n = 5). Technetium 99-m was injected into the left ventricle postoperatively, and the radioactivity of tracheal samples was calculated as a percentage of injected activity/g tissue (%ID/g). The tracheal uptake averaged 1.9 in group CG, and 1.7, 1.3 and 1.5% ID/g in groups PL, TL and TL&PL, respectively. Tracheal transsection (TL) thus reduced the tracheal blood supply by 29.7% compared with the control group (p < 0.05), whereas the reduction of tracheal blood supply following pulmonary hilar ligation (PL) was only 10.9% (n.s.). Tracheal transsection combined with hilar ligation (TL&PL) effected a reduction of 19.9% (n.s.). We conclude that only 10.9% of the tracheal blood supply comes from the pulmonary circulation.