A study of the reaction of several acids with urea resulted in a series of compounds of varying stoichiometry and structure. The acids having the structure H02C(CH2)"C02H produced saltlike compounds with urea when n -0 and 1 and H-bonded complexes for = 2-5. The stoichiometry of all the complexes was 2H2NCONH2-HOOC(CH2)"COOH, except for -1 which had a 1:1 ratio of urea to acid. None of the products was an inclusion compound. From our general observations, we concluded that urea and the dicarboxylic acids are unlikely to form inclusion compounds, and reports of such molecular compounds should be verified by X-ray powder diffraction measurement as well as analysis.2-urea-oxalic acid-2-water. Ljubawin6 in 1872 de-(1) Reprint requests should be addressed to this author at the Pitman-Dunn Research Laboratories.(2) (a) W. Schlenk, Jr., Ann., 565, 204 (1949); (b) L.