In a study on short term memory, 32 educable mentally retarded subjects (mean IQ 62.68, mean mental age 103.78 months) were randomly assigned to each of the four experimental conditions. An automated machine presented the stimuli (32 three-letter words) and the interference items (a list of random numbers read aloud between stimuli presentations). Intervals were 3 seconds, 9 seconds, and 18 seconds respectively for the first time order in which one group read the word aloud (vocal condition) and another group thought it silently (silent condition). The two groups in the second time order were divided the same way but the sequence of time intervals was reversed. M&M candy reinforced correct responses. The predicted depressed curves were obtained for the silent condition with both orders. The main effects of order and vocalization were significant (p .01); the reversed time order groups produced more correct responses and shorter response latencies (p .05); and the vocal condition subjects had the greater number of correct responses (p .05) and a shorter response time (p .01). It is suggested that in forcing subjects to hold material in memory for a longer period of time, a longer storage memory system may have been utilized which functions better for retardates than the short term memory system. (SN)