The effect of ultrasonic treatment of two pseudomonal alginate samples was studied by investigation of their rheological characteristics and interaction with tobramycin, piperacillin and ciprofloxacin. Whilst exposure to ultrasound at an amplitude of 20 microns for 8 min caused a significant decrease in viscosity of both alginates, molecular fragmentation, as demonstrated by PAGE and gel-permeation chromatography, was minimal. Antibiotic penetration was improved substantially however with sonication, leading to a 100% increase in tobramycin and piperacillin diffusion from the alginate compared with an untreated control polymer.