Avocado and soya unsaponifiables (ASU) are plant extracts used as a slow-acting antiarthritic agent. ASU stimulate the synthesis of matrix components by chondrocytes, probably by increasing the production of transforming growth factor-beta (TGF-beta). TGF-beta is expressed by chondrocytes and osteoblasts and is present in cartilage matrix. This study investigates the effect of ASU treatment on the levels of two isoforms of TGF beta, TGF-beta(1) and TGF-beta(2), in the knee joint fluid using a canine model. Twenty-four outbred dogs were divided into three groups. The control animals were given a normal diet, while the treated animals were given 300 mg ASU every three days or every day. Joint fluid samples were obtained prior to treatment, and at the end of every month (up to three months). TGF-beta(1), and TGF-beta(2) levels were measured using a quantitative sandwich enzyme immunoassay technique. ASU treatment caused an increase in TGF-beta(1) and TGF-beta(2) levels in the joint fluid when compared to controls. The different doses did not cause a significant difference in joint fluid TGF levels. TGF-beta(1) levels in the treated animals reached maximum values at the end of the second month and then decreased after the third month, while TGF-beta(2) levels showed a marginal increase during the first two months, followed by a marked increase at the end of the third month. In conclusion, ASU increased both TGF-beta(1) and TGF-beta(2) levels in knee joint fluid.