Physiological cobalamins were separated by means of high-performance liquid chromatography (HPLC). Optimal conditions for elution of methylcobalamin, adenosylcobalamin, hydroxycobalamin and cyanocobalamin were determined. Excellent separation and resolution of these physiological cobalamins by HPLC were achieved. In addition, several cobalamin analogues were also studied and shown to be separable from the physiological forms. HPLC provides a rapid, sensitive, reproducible means of characterizing physiological cobalamins.