OBJECTIVES: I. Determine the tumor response of patients with refractory or relapsed multiple myeloma or Castleman's disease treated with suramin. II. Determine the effects of this regimen on cytokine-mediated symptoms in patients with Castleman's disease. III. Determine the overall and progression-free survival in patients with multiple myeloma or Castelman's disease treated with this regimen. IV. Determine the qualitative, quantitative, and cumulative toxic effects of this regimen in these patients. V. Determine the effect of this regimen on the levels of serum interleukin-6 (IL-6), soluble IL-6 receptor, and soluble gp130 in these patients.