The aim of this literature review is to get a preliminary answer to the problem of the type of information processing deficit of undifferentiated retardates (with an IQ of about 70). Taking the topic of verbal short-term memory as a framework, it appears that children or adults of a subnormal intellectual level can store new information as long as do normals. A difference, however, can be shown in the amount of information which is stored. Generally retardates retain only three to four verbal items while normals memorize seven to nine items. Two explanations are given. First, there is some evidence that subnormals show less rehearsal activity than normals, at least when the former group is not instructed to rehearse. In addition to this functional deficit there appears to be also a structural one. Rehearsal instruction raises the performance, but not to a normal level. It is suggested that retardates cannot encode information into units ofmore than one item, while normals sometimes succeed in memorizing a list ol nine digits into units of three items. Thus, retardates seem also to have a relatively weaker support of long-term memory. Further research is necessary in order to evaluate the information processing system of retardates more in detail.