Production of soluble amyloid peptide precursor (APP) and amyloid peptide (A beta) was measured in CHO cells transfected by the wild-type APP 695 cDNA sequence or by the same sequence carrying missense mutations associated with familial Alzheimer's disease in Sweden. Deletion of the C-terminal domain of the protein corresponding to residues 654 to 695 of APP 695 not only inhibited very significantly the internalization of APP at 37 degrees C, but also led to the secretion of an uncleaved APP in the culture medium of CHO cells. This deletion did not affect A beta production from the Swedish APP but was able to inhibit the production of the wild-type APP. These results demonstrate that, in CHO cells, the internalization of the wild-type APP is needed for A beta production, while the production of the amyloid peptide from Swedish APP is independent of the internalization process.