In two experiments we explored the patterns of attention to semantic and spatial information in younger adults, older adults, and patients with Alzheimer’s disease (AD). In the first experiment, a semantic priming task measured age- and AD-related changes in attentional sensitivity to semantic information. In the second experiment, the semantic priming task was modified to additionally serve as a spatial inhibition of return (IOR) task. The combined semantic and spatial task measured (a) age- and AD-related changes in sensitivity to spatial cues as well as to semantic primes, and (b) interactions between the networks that subserve attention to semantic and spatial information. The results of both experiments revealed group differences in the utilization of semantic primes as a function of prime validity, suggesting that both older adults and AD patients were less likely than younger adults to generate controlled attention-dependent expectancies for semantically related information. Spatial IOR effects in Experiment 2 were evident in the performance of all three groups, but were of reduced magnitude in AD patients. Younger adults’ performance reflected interactions between semantic priming and spatial cuing effects. These findings are consistent with conclusions that (a) selectivity via semantic primes and via spatial cues reflect separate attentional mechanisms, and (b) semantic and spatial aspects of attention are mediated by different but closely interconnected neural networks. Key words: Attentional neural networks, attention deficits, aging. Alzheimer’s disease.