Transforming growth factor-β (TGF-β) receptor-mediated signaling has been proposed to mediate both the beneficial and deleterious roles for this cytokine in amyloid-β protein (Aβ) function. In order to assess receptor dependence of these events, we used PC12 cell cultures, which are devoid of TGF-β receptors. Surprisingly, TGF-β potentiated the neurotoxic effects of the 40-residue Aβ peptide, Aβ-(1-40), in this model suggesting that there may be a direct, receptor-independent interaction between TGF-β and Aβ-(1-40). Surface plasmon resonance confirmed that TGF-β binds with high affinity directly to Aβ-(1-40) and electron microscopy revealed that TGF-β enhances Aβ-(1-40) oligomerization. Immunohistochemical examination of mouse brain revealed that hippocampal CA1 and dentate gyrus, two regions classically associated with Aβ-mediated pathology, lack TGF-β Type I receptor immunoreactivity, thus indicating that TGF-β receptor-mediated signaling would not be favored in these regions. Our observations not only provide for a unique, receptor-independent mechanism of action for TGF-β, but also help to reconcile the literature interpreting the role of TGF-β in Aβ function. These data support a critical etiological role for this mechanism in neuropathological amyloidoses.