To determine the physical and chemical stability of alemtuzumab a high-performance-liquid-chromatography-method was developed. The antibody was stored over 14 days at 6 degrees C, at room temperature and on a vibrating plate and tested by size-exclusion chromatography (SEC) using a phosphate buffer (0.1 M, pH 7) with 0.3 M sodium chloride. The method was also used to quantify alemtuzumab and was validated by parameters such as linearity, range, limit of quantification (LOQ), limit of detection (LOD) as well as precision and robustness. The physical and chemical stability of alemtuzumab could be demonstrated for a time-period of 14 days.