Excretion of thiamine and its degradation product, pyramin, in human urine has been investigated by several authors. Although the excretion of pyramin seems to be proportional to thiamine intake, it has so far been measured only by the fermentation method, and pyramin has neither been isolated in its pure form, nor its chemical constitution proved. Three persons took 50-100 mg each of dibenzoylthiamine daily and urine samples for 8 or 24 hours were collected. In total 56 l urine after the dosage of ca. 4 g dibenzoylthiamine was obtained. It was diluted, adjusted to pH4-4.5 and shaked with an adequate amount of acid clay. The clay was eluted by baryta solution, the acidified eluate was evaporated nearly to dryness and treated with alcohol. The extract was dissolved in water, shaked with hot n-butanol and the butanol solution was poured into a cellulose column. The eluate was divided into 3 fractions by coloring with Dragendorff's reagent or thiochrome reaction and the first fraction was proved to contain 2-methyl-4-amino-5-hydroxymethyl-pyrimidine (OMP) by paper chromatography. Its further purification and concentration were carried out by partition chromatography and finally the presence of OMP was proved by paper chromatography and absorption spectrography, comparing to the authentic specimen of OMP. Also 2-methyl-4-amino-5 (2', 4'-dinitrophenyl)-hydroxymethylpyrimidine was isolated after the incorporation of 2,4-Dinitrofluorobenzene on the alcoholic extract.