Bailey, Smal1, and Ingraham1; Van Wagenen and Liu,3 and Putnam * have reported studies with psychotic populations which suggest that it is possible to predict the effects of prefrontal lobotomy by means of the clinical behavior resulting from procaine-induced narcotization (procaine block) of the prefrontal area. The experiment reported in this paper has been carried out, in part, in an attempt to verify these findings. Since psychological test data may be expected to parallel clinical behavior, a second related question dealt with in the present study is concerned with the degree of similarity between psychological test changes following intracerebral injection of procaine and those following prefrontal lobotomy. Third, an attempt was made to ascertain to what extent clinical changes ascribed to procaine might be due to the other drugs utilized in the operative procedure. The last question was attacked from two points of view: changes in psychological test scores