The study attempts to determine what labor effort disincentives, if any, will result from the introduction of a negative income tax plan into the fiscal structure of the U. S. The study's conclusions are: disincentives appear to be associated with negative income taxation, and these disincentives depend on whether the worker is in the manufacturing or nonmanufacturing industries. And, the disincentive effect for any group of workers is extremely sensitive to the employment opportunities of that group. That is, the groups of workers which should be least influenced by the aggregate employment opportunities show a small response to the proxy used, and the groups of workers which are subject to a wide variation of employment opportunities show no disincentive because their reactions to the tight labor market of 1966 greatly outweigh any disincentives from the proxy. The policy implications would be that, while it is likely workers will exhibit disincentive tendencies under a negative income tax scheme, these tendencies will be greatly outweighed by conditions in the aggregate labor market. In the appendix a complete listing of the regression results is presented for the various subgroups. A four-page bibliography concludes the document. (Author/MW)