This study demonstrates that aqueous humour derived from patients undergoing cataract extraction contains chemoattractants for ocular fibroblasts. The chemoattractant activity is independent of the surgical approach to obtaining the specimen as well as the surgeon operating. Studies in rabbits demonstrate that the chemoattractant activity is not artefactually produced by aqueous sampling and confirm the integrity of the blood-aqueous barrier. Substances responsible for this activity have molecular weights greater than 30,000; they are deactivated by low pH but retain activity at high pH. Identification of the chemoattractants in aqueous humour may allow pharmacological manipulation of would healing in relation to trabeculectomies.