Nonretarded (NR) individuals typically show better short-term memory for brief sequences of auditory than visual information (the modality effect). The present study attempted to determine whether the failure of Down's syndrome (DS) individuals to show the modality effect is due to the verbal-expressive demands of oral responding in memory tasks. DS, NR and MR (non-DS mentally retarded) subjects listened to or looked at increasingly long sequences of digits and attempted to recall them either orally or manually (through placement of items). Analyses suggested the following: (1) manual responding failed to enhance auditory recall in either DS or any other subjects; and (2) difficulty in recalling auditory stimuli was greatest for DS mentally retarded subjects. An additional assessment of DS, MR and NR subjects on a standardized auditory short-term memory test requiring a nonverbal pointing response replicated the above findings.