Human sera were subjected to analytical ultracentrifugation and "high-pressure" gel-permeation chromatography on a system of combined TSK Gel G5000 PW and G3000 SW columns. The chromatographic method produced remarkably superior resolution of the proteins, especially those exceeding 100 000 Da. We calculated the molecular masses of eluted fractions on the basis of their detection by low-angle laser light scattering and their differential refractive index. We discuss the results in relation to the clinical data.