Because of the variable clinical course of multiple myeloma, the identification of prognostic parameters is of clinical interest. Therefore, we analyzed the clinical significance of serum levels of soluble human leukocyte antigen class I molecules (sHLA-I), carboxy-terminal telopeptide of type-I collagen (ICTP), and receptor activator of nuclear factor kappa B ligand (RANKL). Compared with controls, sHLA-I were threefold (p or = 1000 microg/l and ICTP > or = 5 microg/l were significantly associated with a poor overall survival. For RANKL, no significant associations were observed with disease stages, disease status, osteolytic lesions, and survival. In conclusion, sHLA-I and ICTP serum levels seem to be of prognostic significance in multiple myeloma and might be helpful to identify patients of poor prognosis.