An assay method of urinary kinin was described. It consists of extraction of the peptide into n-butanol, re-extraction back to a weak acid solution, concentration under reduced pressure, neutralization and bioassay on the isolated guinea-pig ileum. The method was fairly simple and can be carried out without difficulty. The recoveries and the accuracy proved satisfactory. The method is also specific for the kinin in urine. Ten to thirty micrograms of kinin were excreted daily by healthy persons.