This publication includes plant growth regulatingcompounds evaluated from 1950 to 1958 by the Horticultural Crops Research Branch, Beltsville, Md., under the leadership of John W. Mitchell. Results of tests on the biological activity of 6,545 chemicals for herbicidal, inhibitory, or stimulatory effects are given. The authors have provided (1) the currently correct chemical nomenclature (ChemicalAbstracts, 9th Collective Index, and later approvednames), (2) the Wiswesser Line Notation (WLN), and (3) corrmon designations where applicable for these cOl11Jounds in the "Mitchell file." An index of the common and trade names indicates which chemicals initially evaluated have become economically importantpesticides. The biological and chemical information has been computerized in 34 tables and 3 indexes.