Serum sialic acid (SA) has been reported recently to be elevated in a number of malignant conditions. To test the hypothesis that serum SA may be elevated in patients with multiple myeloma we looked at 34 myeloma patients (17 females and 17 males) and 22 controls (11 females and 11 males). The mean age of the myeloma patients was 61.2 +/- 10.9 years versus 58.9 +/- 12.6 years for the control group. There was a highly significant difference between the serum SA in the myeloma patients compared to the control group; 103.5 +/- 32.8 mg/dL versus 78.9 +/- 10.2 mg/dL respectively (P < 0.001). There was a significant correlation between serum SA and serum total protein and globulin concentration in the IgA myeloma patients, and a significant correlation between serum paraprotein quantity and globulin concentration in the IgM patients.