Reversed-phase high-performance liquid chromatography and capillary zone electrophoresis are widely used in protein and peptide analysis. Degradation of the basic peptide (\left[\right.) Arg (^{6}), D-Trp ({ }^{7,9}), MePhe (\left.^{8}\right])-substance P ({6-) 11 (antagonist G) was monitored with reversed-phase high-performance liquid chromatography, free capillary zone electrophoresis, and capillary zone electrophoresis with a capillary cationic coating. Capillary zone electrophoresis with a dynamically coated capillary provided better separation between antagonist (G) and its degradation products (formed at (\mathrm{pH} / \mathrm{H}). 13) than high-performance liquid chromatography and free zone capillary electrophoresis. Rate constants of the alkaline degradation of antagonist (G) measured with reversed-phase high-performance liquid chromatography and capillary zone electrophoresis with a dynamic coated capillary wall are similar whereas the values measured with free zone capillary electrophoresis are lower. Rate constants for the degradation of antagonist (G) in acidic media are comparable for the three techniques. It is concluded that capillary zone electrophoresis using a dynamic coating with Fluorad is the most suited of the above-mentioned techniques in analyzing antagonist (G) and its degradation products. & 1994 Academic Press. Inc.