1. The literature relating to the testing of organic compounds for growth- regulating activity on plants has been reviewed chronologically. 2. Three methods have been devised, whereby inhibitory activity at high dilution can be determined and evaluated. All depend on elongation or weight changes subsequent to treatment. The activity of the compounds under test are expressed as a percentage of the inhibition brought about concurrently by 2,4-dichlorophenoxyacetic acid as a common reference material. The plant materials used are germinating corn and young kidney-bean plants. 3. One thousand and sixty organic compounds, almost all synthesized expressly for this work, were submitted to test by the three methods. The data obtained have been assembled in groups on the basis of activity in reducing elongation of the primary root of germinating corn as compared with the reference material. 4. The significance and interpretation of the tests are discussed. Compounds showing high activity are indicated as promising for use as herbicides.