Here we show that certain c-hGH batches to which patients with iCJD and Aβ pathology were exposed have substantial levels of Aβ<sub>40</sub>, Aβ<sub>42</sub> and tau proteins, and that this material can seed the formation of Aβ plaques and cerebral Aβ-amyloid angiopathy in intracerebrally inoculated mice expressing a mutant, humanized amyloid precursor protein.