The effect of intratendineous injections of polysulphated glycosaminoglycan (PSGAG) as treatment of collagenase-induced tendonitis was studied. Two groups (GI and GII) of five Arabian horses each, males and females, two to six year-old, were submitted to experimental tendinitis of the superficial digital flexor tendon of the left thoracic limb by intratendineous injection of 1.0ml of collagenase (2.5mg/ml). Seven days after the induced-lesions were created, the horses of GI received five intralesional injections of 1.0ml (125mg) of PSGAG, every four days. Horses of GII received injections of saline in the same dose and rate. Clinical and ultrasonographic evaluations were performed periodically, during 150 days. All animals showed lameness, increased local pain, heat and swelling 24 hours after the injury was created. All signs, except to swelling, which remained visible by the end of the study, showed regression in all animals. Lesions of variable size, shape and position were evidenced by the ultrasonographic evaluation, reaching maximum severity between the seventh and the 23 rd days. By the end of the study, the echogenicity grade ranged from 1 to 2, and the grade of fiber alignment from 0 to 2. The histopathologic analysis demonstrated repair areas with intense fibroplasia and neovascularization, collagen fibers poorly organized, and thickened hypercellular endotenon. The data of this study did not show significant differences between the treated and control groups, therefore leading to the conclusion that the intralesional injection of PSGAG did not have beneficial effects in the treatment of collagenase-induced tendinitis.Keywords: polysulphated glycosaminoglycan, tendinitis, equine RESUMO Estudou-se o efeito de aplicações intratendíneas do polissulfato de glicosaminoglicanas (PSGAG) no tratamento de tendinite induzida pela colagenase. Dois grupos (GI e GII) de cinco eqüinos da raça PuroSangue Árabe, machos e fêmeas, com idades entre dois e seis anos, foram submetidos à tendinite do tendão flexor digital superficial do membro torácico esquerdo por aplicação intratendínea de 1,0ml de colagenase (2,5mg/ml). Decorridos sete dias da indução da lesão, os eqüinos do GI receberam cinco aplicações intralesionais de 1,0ml (125mg) de PSGAG, a intervalos de quatro dias, enquanto que os do GII receberam aplicações de solução fisiológica em igual volume e freqüência. Efetuaram-se avaliações