To investigate the level of nitric oxide (NO) in aqueous humour after excimer laser keratectomy in guinea pigs. Methods: NO levels of the aqueous humour were measured by nitric oxide analyser with chemiluminescence assay in three Groups. Group I served as control, 10 m$mu$ excimer laser corneal photoablation was performed in Group II and 20 m$mu$l corneal photoablation in Group III. Results: NO levels of all groups showed no difference when compared to the control (p>0.05). Conclusion: Excimer laser keratectomy did not change the NO level of aqueous humour in guinea pigs 24 hours following photoablation and this finding could be explained by increased transforming growth factor-$beta$1, (TGF-$beta$1) level of aqueous humour after excimer laser therapy.