The separation method of serum proteins was established with an untreared 50 microns i.d. x 47 cm (40 cm to detector) capillary and detection of absorbance at 200 nm. Analysis was performed by pressure injectction 17.23 kPa.s and by applying 23 kV in the constant voltage mode. Serum samples were diluted 40-folds with assay buffer (12.5 mmol/L sodium borate, 1 mmol/L calcium lactate, 0.7 mmol/L magnesium sulfate, 1 mmol/L EDTA were mixed). A normal control serum protein was separated into 6 fractions. In pregnant serum, the alpha 0 was an additionally unknown fraction. Comparison of capillary electrophoresis with conventional cellulose acetate electrophoresis for analysis of serum proteins from normal control, pregnant women multiple myeloma and tonic rachitis patients indicates that capillary clectrophoresis is a new technique for the analysis of serum proteins because of its high efficiency, on-line data processing and automation. Capillary electrophoresis is the reliable technique for clinical diagnosis of serum protein abnormalities.