Pro-inflammatory cytokines interleukin-6 (IL-6), interleukin-1beta (IL- 1beta), tumour necrosis factor-alpha (TNF-alpha) and chemokine interleukin-8 (IL-8) may play a significant role in the regulation of bacterial corneal infection. The aim of this study was to investigate the gene expression of these four mediators in a human corneal epithelial cell line challenged with Pseudomonas aeruginosa within 12 h. Human corneal epithelial monolayers were colonized with P. aeruginosa strains Paerl, 6206 and 6294. Expression of IL-6, IL-8, IL-1beta and TNF-alpha was analysed using semi-quantitative reverse transcription-polymerase chain reaction. Results showed that both IL-6 and IL-8 mRNA were expressed very early (4 h) during bacterial colonization and remained at high levels until the end of the experiment. Expression of IL-1beta and TNF-alpha mRNA appeared at 8 h after bacterial stimulation. No expression of IL-8, IL-1beta and TNF-alpha mRNA was observed in unstimulated cells. Interleukin-6 mRNA was expressed at low levels in unstimulated cells. In conclusion, bacterial colonization of human corneal epithelial cells induced expression of IL-6 and IL-8 mRNA earlier and at higher levels than IL-1beta and TNF-alpha mRNA.