Inhaled aerosol drugs are limited in their ability to reach all regions of the lung when altered ventilation patterns exist, as associated with cystic fibrosis. This can cause inhaled drugs to deposit non-uniformly so that some lung regions receive very high local doses of medication while other regions go untreated. In an infected lung, this can result in a reservoir of infection that is never effectively treated by the therapy. In vivo studies have suggested that the inclusion of surfactant in a drug formulation may enhance spreading through Marangoni flow. To explore how surfactants might impact spreading across lung airway surfaces, the spreading of aqueous surfactant solutions on aqueous solutions of porcine gastric mucin was investigated using long working distance video microscopy and inert particulate tracers. For a fixed volume of surfactant solution, the area spread increased with the inclusion of surfactant in the spreading liquid and showed a concentration dependence, suggesting Marangoni flow. However, spreading results indicate that the mechanism may not be simply Marangoni since tracer particles far from the surfactant front moved immediately upon surfactant deposition, and the particles also recoiled at long times. To investigate these results which are not consistent with Marangoni driven spreading on a simple fluid, spreading experiments were performed on simpler subphases comprising aqueous polyacrylamide solutions. The results showed the same behavior, suggesting that surface elasticity or some other property of the polymer solution/air interface may play an important role in the spreading process. Control experiments were performed using ethylene glycol as the subphase. Ethylene glycol provides a similar surface tension as the polymer solution subphases and it also is miscible with the aqueous surfactant solutions but it lacks the entangled polymeric characteristics. Surfactant solutions did not spread on the ethylene glycol but penetrated into the bulk of the solution, suggesting that the polymeric nature of the subphase is important for inhibiting the transport of overlaid solutions into the subphase relative to their spreading across the surface of the subphase. In this talk, we will present results from spreading experiments, surface tension measurements and x-ray reflectometry experiments that suggest the mechanism of enhanced spreading on mucin solutions is not simply Marangoni driven flow.