The viscoelastic properties of canine tracheal secretions obtained via a chronic pouch preparation have been determined. Storage and loss shear moduli were measured both for whole unfractionated material and for fractions collected from an agarose gel column. Of the two major carbohydrate and protein containing peaks, the one eluting first and containing carbohydrate-rich glycoproteins determined essentially all the rheological behavior of the secretions. The retained peak materials containing “serum-type” glycoproteins possessed no clastic behavior.