The two mltabolites of caffeine, 5 - acetylamino - 6 - formylamino - 1 - mlthyhuracil (AFMU)and 1 -mlthylxanthine(IX),in urine collected from 190 health Chinese volunteers were analyzed by HPLC. The peak height ratio of AFMU/IX was used to determine the acetylators phenotypes. The results showed that 73. 68% of the subjects could be classified as fast acetylators which is similar to the ratio previousy reported for Asian with isoniazide and sulfamlthazine as the pharmacological probes. Phenotyping with caffeine as a probe via analyzing its urinary metabolites by HPLC is shown to be simple and fast. The analyzing precision is (CV% )2. 2% - 4. 4% and the rate of recovery is 94% - 95 %.
