The amount of protein that excreted in normal human urine is insignificant and it attained to about 20∼40 ㎎ per day. It probably consists of serum albumin, serum globulin and some enzymes from blood, with molecular weight up to 80,000. A peculiar protein, the Bence-Jones protein, is also eliminated in urine by some patient having multiple myeloma. The histones whose molecular weight is estimated to be 11,000∼21,000, the basic protein of the genetic material, are reportedly absent in human and horse sera (G. Patin: J. Pharm. Chim., 1913). It is the purpose of this paper to report the isolation of histones from human urine and the characterization of some properties of histone fractions. A total of 20ℓ of freshly collected urine from healthy male high school students was cooled quickly and maintained at 5℃ until enough urine is collected for foaming. After vigorous agitation of the urine, the foam layer was collected and this procedure was repeated. The foam was then liquefied by the addition of a minimal amount of octyl alcohol. Histones were precipitated from foam concentrate by adding ammonium sulfate to 60%saturation and further fractionation was followed by the procedure of Johns and Philips. A total of 72 ㎎ of whole histone was recovered from 18ℓ of urine. The relative amounts of 5 major fractions of urine were compared with the corresponding fractions of thymus and liver of calf. It is interesting to note that the relative amounts of the 5 major histone fractions in urine were remarkably similar to the thymus and liver of calf. Analysis of amino acid composition was conducted on the individual histone fractions from urine. This analysis established that a striking constancy did exist throughout all corresponding fractions between urine samples and thymus and liver of calf. This finding suggests that the histones from human urine and calf thymus and liver seem to be homogeneous protein. The physiological significance of histone excretion in urine remaines to be clarified.