Results indicate that AD and PD patients are more impaired on odor identification and recognition tasks than on odor detection thresholds task. In addition, PD patients are more impaired on detection thresholds than AD patients. These results suggest that PD patients are more impaired on low-level perceptual olfactory tasks whereas AD patients are more strongly impaired on higher-order olfactory tasks involving specific cognitive processes. The effect appears more pronounced for AD than PD, which seem to be affected more homogeneously. In conclusion, olfactory identification and recognition appear as the most interesting candidates to be included in a battery to detect subclinical cases in AD. In parallel, detection thresholds should be included in such a battery for subclinical PD patients.