SUMMARYMethods for the preparation of pigments from thiobarbituric acid and oxidized milk fat, malonaldehyde, and 2‐sulfanilamidopyrimidine are presented, and the general characteristics of the pigment preparations are described. Various oxidized vegetable oils were found to react with thiobarbituric acid to produce the characteristic red color. The chromatographic adsorption techniques investigated did not prove satisfactory for isolation and purification of the pigment preparations. Attempts to form chemical derivatives were unsuccessful, and the solubility characteristics of the pigments prevented the determination of molecular weights by colligative properties. Elemental analyses of pigment preparations were not sufficiently consistent to justify definite conclusions.A spectrophotometric technique permitting calculation of the stoichiometry of the malonaldehyde‐thiobarbiturie acid pigment is presented. Results suggest an equimolar reaction without loss of water. Other spectral data indicate the pigment is degraded to yield equal quantities of malonaldehyde and thiobarbituric acid. A second malonaldehyde‐thiobarbiturie acid pigment with an absorption maximum of 507 mμ was isolated. The spectral techniques indicated a combining ratio of 3 aldehyde molecules to 1 thiobarbituric acid molecule for this p