The present invention discloses a double transgenic fly that expresses both Tau protein and the human Aβ42 peptide of human amyloid-β precursor protein (APP). The double transgenic flies of the present invention display a synergistic altered phenotype as compared to the altered phenotype displayed by transgenic flies expressing either Tau or human Aβ42 alone, and thus provide for an improved model for neurodegenerative disorders, such as Alzheimer's disease. The invention further discloses methods for identifying for therapeutic compounds to treat neurodegenerative disorders using the double transgenic flies.