Tracheal mucociliary clearance studies, mucus collections, and rheologic studies were performed on a weekly basis in 7 adult purebred beagles in an attempt to correlate clearance rate with rheology of mucus. Clearance rates were determined by a percutaneous transtracheal, radioisotope injection technique. Mucus was collected from dogs equipped with a tracheal pouch, and rheologic determinations were performed on a dynamic microrheometer. Individual analysis of data for each dog failed to reveal any significant relationship between clearance rate and any parameter of elasticity or viscosity. However, when data from all 7 dogs were pooled, covering a much wider range of the measured variables, it was seen that as the elastic modulus increased, the rate of clearance decreased. The mucociliary clearance rate was halved by an approximate ten-fold increase in elastic modulus of mucus.