Serum concentrations of acute-phase-proteins C-reactive protein (CRP), alpha 1-antitrypsin (AAT), alpha 1-acid glycoprotein (AGP) as well as levels of immunoglobulins G, A and M and of complement components C3 and C4 were evaluated in 15 patients with advanced (stages III and IV) Hodgkin's disease. Of these patients 9 suffered from B symptoms including pruritus, night sweats and fever. While all patients had highly increased concentrations of CRP and AAT and 11 patients also had elevated levels of AGP in their sera, these concentrations were significantly (P less than 0.001) reducible by the administration of chemotherapy. Patients with B symptoms also had significantly higher concentrations of CRP (P less than 0.02), AAT (P less than 0.05) and AGP (P less than 0.05) in their sera than patients without. Plasmapheresis which was performed in 3 patients did not achieve a long-lasting reduction of serum concentrations of any acute-phase-protein tested. Complement components C3 and C4 exhibited a similar behaviour as acute-phase-proteins in that they were elevated in patients with B symptoms and reducible by the administration of chemotherapy (P less than 0.001 and P less than 0.02, respectively). We conclude that serum concentrations of CRP, AAT and AGP can serve as useful markers for the assessment of tumour activity in patients with advanced Hodgkin's disease. Whereas the concentrations of immunoglobulins G and A in patients were comparable to normal controls, IgM was significantly (P less than 0.05) reduced in patients who had received chemotherapy, but not in those who were newly diagnosed and had not received any treatment. Thus, chemotherapy lowered serum concentrations of IgM without influencing levels of IgG and IgA.