An investigation was made to discover the number of stimuli that Ss could usefully remember in a simple stimulus-response task. The problem was to press a button at the right time in relation to the stimulus. S had to remember a continually changing small groups of letters. Ss required approximately 1 sec. per stimulus for each member of the group which they had to hold in memory. (PsycINFO Database Record (c) 2006 APA, all rights reserved)