Soluble isoforms of various adhesion molecules have recently been observed in the blood circulation, but the physiological effects of such molecules remain unsettled. Our earlier results indicate that soluble CD44 can be detected in sera of healthy individuals and that significantly higher levels of serum CD44 (s-CD44) can be found in lymphoma patients. The serum level of the standard form of CD44 parallels the clinical treatment response in patients with lymphoma. In the present study, we have investigated the clinical significance of s-CD44 in non-Hodgkin's lymphoma measured at the time of the diagnosis. S-CD44 was measured from the sera of 123 patients with non-Hodgkin's lymphoma by dot blotting High levels of s-CD44 were associated with high serum levels of lactate dehydrogenase and thymidine kinase, high histological grade of malignancy and poor overall survival. However, s-CD44 level did not have independent prognostic value in a multivariate analysis. In conclusion, a high s-CD44 level at the time of diagnosis was associated with poor survival and several other adverse prognostic factors. Our previous and present studies taken together suggest that measurement of s-CD44 is a valuable tool to monitor treatment response in lymphoma patients. However, it may not be an improved prognostic marker.