In the present study, were examined the inhibitory effect of erythromycin on the biofilm formation by a temperature-sensitive mutant (Ts25) of Pseudomonas aeruginosa N-42 on the surface of Ishikawa cells which can produce a mucin-like glycoprotein physicochemically similar to mucoproteins produced in the human airway. Usually, 38-45 microcolonies (biofilms) were formed after 10 days of incubation in cultures of Ishikawa cells and P. aeruginosa Ts25. Erythromcin suppressed the adhesion to Ishikawsa cells of P. aeruginosa and its subsequent biofilm formation at doses as low as 0.2 microgram/ml. Erythromycin also exhibited the suppressive effect on the production of glycoproteins by Ishikawa cells at doses higher than 1 microgram/ml and the production of elastase and exoenxyme A from P. aeruginosa at doses higher than 2 micrograms/ml. These results suggest that erythromycin can inhibit the biofilm formation in culture of human epithelial cells and P. aeruginosa and the in-vivo bacterial biofilm formation may be attributed to host cell-derived factors rather than bacterial products.