Abstract: 1. The hyoscyamine and hyoscine contents of the dried flowers of certain Datura species known as Yang-ching-hwa in Peking drug stores have been determined by a modified partition chromatographic method and the details are described. 2. The total alkaloids present in the flowers are found to be about 0.26%, of which 82.5% is hyoscyamine. 3. The distribution of alkaloids in different parts of the flower was determined by a microchemical method using Wagner’s reagent as the precipitating agent. 4. The highest alkaloidal content was found in the carolla part, followed by the calyx; the receptacle and peduncle contain only traces. 5. It is recommended that the Yang-ching-hwa might be used as a source of hyoscyamine.