To treat body surfaces, such as the sinuses, which are coated with biofilms, the surface is irrigated and suctioned with a fluid which may contain a biocide or other chemical agent for disrupting the biofilm while ultrasonic energy is applied to either the fluid barrier formed over the biofilm or a body surface proximal to the biofilm. Action of the fluid enhanced by the ultrasonic energy tends to remove sections of biofilm which are suctioned out of the site. An electrical field may also be applied to the biofilm to enhance the disruptive action. Apparatus for practicing this method to treat chronic rhinosinusitis comprises an elongated tube adapted to be inserted into sinus cavities through the nose or mouth. The tube includes a first lumen which feeds an irrigating fluid containing biocides and/or biofilm-disruptive chemicals to the treatment site and a second lumen which suctions fluid from the site. An ultrasound horn extends through the tube and its distal end introduces ultrasonic energy into the fluid layer overlying the biofilm. Alternatively, an ultrasound probe may be applied to an adjacent body surface, such as the face over a sinus cavity. In an alternative embodiment, the tube includes a pair of electrodes which establish an electric field across the biofilm, accelerating degradation.