Four neocortical regions (frontal, parietal, temporal, occipital) of 44 cases were impregnated by a silver stain to show neuritic plaques and stained with Congo red to show amyloid plaques. In 11 cases with large numbers of argentophilic plaques these plaques decreased significantly with age while the reverse appeared to be true for the congophilic plaques. In the remaining 34 cases which had few argentophilic plaques the numbers of congophilic plaques increased significantly with age in the parietal and occipital regions. These results suggest that the neuritic component of senile plaques precedes the amyloid cores in their pathogenesis although a causative relationship is not implied.