We examined the differences in tracheal mucus rheology between nonsmokers and smokers, and between smokers with and without lung cancer. Mucus was collected from patients undergoing diagnostic bronchoscopy without atropine by holding a cytology brush in contact with the tracheal mucosa for 10 to 15 s. Samples were obtained from 43 patients 24 to 79 yr of age: nine nonsmokers, 18 current smokers, and 16 exsmokers (greater than 6 months); 12 patients (nine smokers, three exsmokers) had lung cancer. Pulmonary function testing showed that the nonsmoker patients had significant restrictive lung disease, and the patients with cancer had significant irreversible airway obstruction. The viscoelastic properties of the mucus samples were determined by magnetic microrheometry. Two parameters are reported: G* (modulus of rigidity) and tan delta (loss tangent), each measured at 1 and 100 rad/s. G* is an index of overall deformability (elastic and viscous), and tan delta is the ratio of viscous to elastic deformability. For nonsmoker patients, the viscoelastic parameters were virtually identical to those found previously for normal volunteers. For smokers without cancer, the mucus had a lower value of tan delta 1 rad/s and therefore was predicted to be more easily transportable by ciliary action; for exsmokers without cancer, ciliary transportability as calculated from viscoelasticity was even higher because of both low tan delta and low G*. Mucus from patients with cancer was not significantly different from that of nonsmokers; however, the mucus was predicted to be less easily clearable by ciliary action than was that from smokers and exsmokers without cancer, mainly because of a higher tan delta at 1 rad/s.(ABSTRACT TRUNCATED AT 250 WORDS)