We used rabbit antisera to the 210,000; 155,000; and 70,000 mol. wt. neurofilament - polypeptides and monoclonal antibodies (BF 10; RT97) known to react with human neurofilaments in an immunohistochemical study of neuronal changes in Pick's disease and in senile dementia of the Alzheimer type. Pick bodies as well as neurofibrillary tangles and neurites showed strong reactivity with the monoclonal antibodies but remained unlabeled when treated with the rabbit polyclonal antisera. Our results indicate that the stained material in Pick bodies share antigenic determinants with neurofibrillary tangles and neurofilaments.