Presented 5 memory letters either auditorily (in a male voice), visually, or both auditorily and visually while 36 Ss shadowed female-voiced letters. A simple additive formula was used to predict recall performance following concurrent visual and auditory presentation. The formula accurately predicted performance for immediate recall, indicating independent visual and auditory storage systems for very brief time periods. However, following retention intervals of 2, 6, and 20 sec., the predicted scores were higher than those actually observed. Deviations from the formula at the longer retention intervals are explained by assuming (a) the existence of a limited duration precategorical acoustic storage system, and (b) that rehearsals were primarily visual. (PsycINFO Database Record (c) 2006 APA, all rights reserved)