Ligneous conjunctivitis in a horse: a case of eleven months duration a six months old throughbred female race horse was received presenting events of mucous purulent discharge from the right eye for two days. close examination of both eyes revealed bilateral mucous purulent conjunctivitis, more severe on the left eye where discharge was more profuse, with tarsal and bulbar chemosis and blepharospasm. this animal also had a fluoresceine fixing superficial linear ulcer on the left eye. it was performed culture of material from the botton of conjunctive sack, which revealed an infection by pseudomonas spp, sensitive to tobramycine. based upon microbiological tests, tobramycine eye drops (15 mg/ml) and ophtalmic ointment (15 mg/g) was given for three weeks, and a two percent atropine and one percent dichorphenac eye drops were given for five days. at the end of the treatment, the right eye was calm and without alterations while the left eye displayed a tarsal membranous conjunctivitis with minimal serous ocular discharge. the presence of an allergic conjunctivitis was suspected and four percent dissodium chromoglicate eye drops were given. in spite of the decrease of inflamation observed, the conjunctive membranes remained. surgical débridement of the membranes was performed and representative material was collected and sent for histological examination. based upon human and canine reports and histological findings, the most probable diagnosis was ligneous conjunctivitis. after biopsy, the drug chromoglicate was replaced by one percent prednisolone eye drops for three weeks. after this, the eye showed a discreet dorsal tarsal chemosis and hyperemia but no membranous conjunctivitis. as supporting therapy a daily morning instillation of corticoid for 30 days was ordered. five months later, a recurrence of the membranous conjunctivitis was verified and these membranes invaded the cornea, causing temporal pigmentary keratitis. a two percent cyclosporine ointment was then given and a new biopsy asked. the diagnosis of recurrent severe ligneous conjunctivitis was evident, and a wide surgical resection of the membranes and vascular cauterization was decided. postoperative treatment was composed by one percent prednisolone, one and a half percent tobramicine eye drops together with 5,000 iu /ml heparin. treatment proceeded for 30 days when the antibiotic was taken off, corticoid frequency was reduced and topic heparin kept. ligneous conjunctivitis is a chronic membranous conjunctivitis with presence of membranes mainly in the tarsal superior conjunctives, of ignored etiology. up to the present, two months after the surgical resection of the membranes, the topical use of corticoid and heparin satisfactorily controls the case, now eleven months old. key words: horse, ligneous conjunctivitis, heparin