Résumé : The density of senile plaques in 15 women over 75 years of age was higher when evaluated by thioflavine S than by immunocytochemistry with a polyclonal antibody against paired helical filaments. Mental status had been prospectively assessed in this cohort by the test score of Blessed et al. A difference between the two methods was found whatever the degree of mental impairment. Senile plaques were exceptionally immunolabeled in the least affected cases. This could not be explained only by differences in sensitivity of the stains and suggests that the amyloid is surrounded by anti-PHF positive neurites only in the latest stages of the senile plaque.