Proteolytic enzymes can act on the polymeric structure of the bronchial mucus, shortening the long chain of mucoproteins, DNA and other macromolecules, and thus reducing the viscosity of the mucus facilitating its expectoration. Seaprose (Flaminase, Puropharma) belongs to this class and is a proteinase from Aspergillus melleus and it is mainly used in traumatology, orthopaedics, gynaecology and pneumology. In the present study the in vitro activity of increasing concentrations (0.25, 0.5, 1%) of seaprose incubated with bronchial mucus samples (1 ml) was investigated by a rheological technique (transient test) that assesses changes in viscosity and elasticity. A dose-effect relationship between increasing concentrations of seaprose and the corresponding reductions in bronchial mucus viscosity was found. There was also a parallel reduction in elasticity after incubation with 0.5%, but an unfortunate distribution of values for 0.25 and 1% concentrations does not allow us to state whether there is a dose-effect relationship for elasticity.