• The chemoattractant activity for ocular fibroblasts of the aqueous humor of patients undergoing glaucoma surgery was evaluated in 48-well microchemotaxis chambers and compared with control specimens from patients undergoing cataract extractions. All specimens were chemoattractant, but those from patients who had previously undergone glaucoma surgery that had failed were of significantly greater activity than the controls'. This chemoattractant activity is primarily chemotactic. It consists of heat-stable and heat-labile components. The predisposition of a patient to sustain failed glaucoma drainage surgery may be related to the chemoattractant activity of his aqueous humor, since strongly chemoattractant aqueous humor may encourage fibrosis at the operation site.