Several authors have demonstrated the pivotal role of proinflammatory cytokines in inducing progressive cartilage degradation and secondary inflammation of the synovial membrane in osteoarthritis (OA). It has recently been established that tumor necrosis factor (TNF)-alpha plays a well-defined role in the pathophysiology of inflammatory joint diseases and that binding to circulating soluble TNF-alpha receptors can inactivate it. We investigated the influence of mud pack treatment, which is able to diminish TNF-alpha serum values, on specific TNF receptor (sTNF-R) levels. Thirty-six patients with OA were enrolled and randomized into two groups. Group A underwent mud pack treatment and group B underwent thermal bath treatment. A group of 20 healthy untreated subjects was used as a control. Blood samples were collected at baseline and after treatment, and assays of sTNF-R55 and sTNF-R75 were performed in both groups. We found small changes in sTNF-Rs serum values but these were not statistically significant. sTNF-R55 serum values decreased by 0.4% after the therapy in group A, while in group B the decrease was -17.7%. sTNF-R75 was reduced by -21.17% in group A and by -10.6% in group B. In conclusion, through its thermic and ant/inflammatory activity mud pack treatment shows complex interaction with the most common factors of inflammatory and cartilage degradation. Our results suggest that the thermic component of this natural treatment is mainly involved in modulating inflammatory reaction and cartilage damage through binding of the circulating TNF, which controls the activation of the cells responsible for the production of proinflammatory cytokines.