To determine whether the secretory pathway of beta/A4 amyloid protein precursor (APP) was altered in familial Alzheimer's disease (FAD) with a mutation of Val717 to Ile, cerebrospinal fluid was studied by Western blotting. The ratio of the density of the bands labeled with the antibody against the amino-terminal part of beta/A4 protein to that with the antibody against amino-terminal part of beta/A4 protein to that with the antibody against amino-terminal part of APP was not decreased. The present result suggests that the secretory pathway is not altered by the mutation in such a way that amyloidogenic full-length beta/A4 protein is generated.