The matrix protein tenascin-C (TN-C) is present in the blood of healthy individuals at concentrations around 1 mg/l. Elevated serum levels have been reported in cancer patients. In this study we have measured the concentration of circulating TN-C in 40 patients with melanoma, soft-tissue sarcoma (STS) or squamous-cell carcinoma (SCC) of the limbs, and have found a minor increase in the mean concentration compared with healthy subjects. Only 10 patients had TN-C levels above the normal range. No correlation was observed between TN-C levels and tumor burden. Nineteen patients were treated by isolation limb perfusion (ILP) with TNF, IFN gamma, melphalan (11 melanoma, 2 SCC and I STS), melphalan alone (3 melanoma) or hyperthermia at 41.5 degrees C (2 melanoma). ILP with TNF, IFN gamma and melphalan induced a rapid increase in plasma TN-C levels, peaking in most patients between 24 or 48 hr after ILP. Two patients treated with hyperthermia only had a slow increase in TN-C concentration peaking at day 4, while the patients treated with melphalan alone had no significant change. In some cases elevated TN-C levels persisted for over 8 weeks after ILP. The early rise in TN-C concentration correlates with the increase in circulating C-reactive protein. Our findings suggest that circulating TN-C behaves, at least in part, as an acute-phase protein and that it may play a role in the inflammatory response.