St/mmary.-This study was designed as one test for the assumption made by B. F. Skinner and other authors of programmed material rhat vanishing textual stimuli increase the efficiency of memorization. 34 fourth grade pupils were differentially treated using vanishing textual stimuli as the variable. The difference in retention between the two groups was not significant.The omission of verbal stimuli in textual material has taken at least three forms since the onset of applied operant conditioning theory.One form of omission was described by Skinner ( 1961, pp. 389-390) as a procedure for teaching through using what he termed "vanishing texmal stimuli." Skinner argued that a machine (or, by inference, a program) could do in a controlled way what the learner normally does when he is memorizing a passage or an image-avert the eye as learning progresses. This method can be described as the successive omission of parts of a whole. For example, words or parts of words can be successively removed from any written material. The assumption underlying this technique is that the learner in overtly or covertly filling in the missing parts will inccease the efficiency of his learning.A second or related form of omission employed by writers of learning materials is that of dropping from the sequence of repeated items a stimulus question or expression that has been correctly responded to previously by the learner. Rothkopf (1961) compared the effects of dropping an item after two correct responses with dropping an item after one correct response. While there was no significant difference between the two methods, the assumption that some omission of materials possessed. an intrinsic superiority over no omission was not challenged.A third form of omitting material derives from the assumption made by psychologists in operant conditioning and programmed text writers that overt responding is more efficacious than covert responding. This idea was promoted by Skinner (1954) and has been supported by many others. This idea has led to the practice of leaving blank spaces in verbal material with directions to the learner to make a definite overt response to the whole, usually by writing down the word that should fiit into the blank or blanks. ( A component of this method is reinforcement of the correct response by exhibiting the desired response after the learner has made his response; cf. Holland and Skinner, 1961.) While the asumption behind this approach to teaching recently has been both questioned (e.g., Stolurow, & Walter, 1762; Keislar, & McNeil, 1962) and 'The investigator is grateful to Dr. Douglas T. Kenny of the Graduate School of Education, Harvard Universitv. for having asisted him in desienine this ex~eriment. Acknowledeement is also made ;b the ~e l r & e (Massachusem) ~r h o o r~y s t e m lor permission to condE;r the study there.