A simple Pseudomonas aeruginosa G48 biofilm on stainless steel discs provided a useful primary screen of potentiating effects of various permeabilizing agents on antibacterial agents. Experiments with Ps. aeruginosa suspensions could not be used to predict the effects of biocides and permeabilizers on biofilms. Although antibacterial activity against biofilms was less than demonstrated in suspension tests, potentiation by some permeabilizers was still observed.