Background and Objectives - After exposure to indomethacin, human umbilical vein endothelial cells have shown increased procoagulant activity. Thrombosis in rabbit auricular veins has been observed after injection of tenoxicam with its diluent or of the diluent alone. Human studies evaluating venous endothelium after tenoxican injection were not found in the literature. This study aimed at evaluating whether tenoxicam with 0.9% sodium chloride changes the venous endothelium of rabbits as it is observed when associated to its diluent (bidistilled water). Methods - The study involved 90 rabbits (2000 and 3500 grams) divided in two groups: Control group, which received 0.9% NaCl; Experimental group, which received tenoxicam (20 mg) with bidistilled water or with 0.9% NaCl. A constant volume of 2 ml was administered to both groups. Anesthesia was induced with acepromazine maleate, ketamine hydrochloride and xylazine hydrochloride, and the puncture of right and left caudal auricular veins was performed with a 27G butterfly needle. Animals were confined for 6 hrs, 12 hrs, and 24 hrs, when they were once more anesthetized and sacrificed, with extraction of the auriculae at their base, followed by microscopic venous study. Results - Thrombosis was observed in 19.4% of the Experimental Group after the administration of tenoxicam with bidistilled water and in 22.2% after the administration of tenoxicam with 0.9% sodium chloride. In the Control group, which has only received 0.9% sodium chloride, no thrombosis was observed. Conclusions - It was possible to conclude that tenoxicam, either with bidistilled water or 0.9% sodium chloride, has induced thrombosis in the veins it was injected.522223230Nygard, G., Hudson, M., Mazure, G., Procoagulant and prothrombotic responses of human endothelium to indomethacin and endotoxin in vitro. Relevance to non-steroidal anti-inflammatory drug enteropathy (1995) Scand J Gastroenterol, 30, pp. 25-32Schnaider, T.B., Andrade, C.H.V., Juliano, Y., Estudo histopatológico do efeito do tenoxicam e do seu diluente no endotélio venoso, em coelhos (2000) Acta Cir Bras, 15, pp. 118-123Cotran, R.S., Kumar, V., Robbins, S., (1996) Robbins Patologia Estrutural e Funcional, 5 a Ed., pp. 84-109. , Rio de Janeiro, Guanabara KooganWhittle, B.J.R., Morishita, T., Ohya, Y., Microvascular actions of platelet-activating factor on rat gastric mucosa and submucosa (1986) Am J Physiol, 251, pp. G772-G778Wallace, J.L., Keenan, C.M., Granger, D.N., Gastric ulceration induced by nonsteroidal anti-inflammatory drugs is a neutrophil-dependent process (1990) Am J Physiol, 259, pp. G462-G467Wallace, J.L., Lipid mediators of inflammation in gastric ulcer (1990) Am J Physiol, 21, pp. G1-G11Rang, H.P., Dale, M.M., Ritter, J.M., (2001) Farmacologia, 2 a Ed., pp. 255-269. , Rio de Janeiro, Guanabara Koogan