Four experiments investigated the ability of young (18 to 27 years) and older (59 to 76 years) adults to perform visual search and tone detection concurrently. In each experiment, the proportional increase in tone reaction time (RT) on the dual-task trials, relative to a tone-only baseline, was greater for older adults than for young adults. In contrast, the changes in tone RT that occurred as a function of the temporal interval between the tone and the visual display were similar for the young and older adults in each experiment. The age differences in tone-detection performance appeared to represent an age-related reduction in a processing resource, such as attentional capacity or effort, that is distinct from processing speed. This age-related reduction in attentional capacity was evident in the encoding and response selection processes required by the visual-search task, and in the use of advance information for improving search performance. © 1997 Elsevier Science Ltd. All rights reserved.