The association of myasthenia and Biermer's anemia is very rarely reported. In a series of 138 cases of myasthenia, this association was found in only one patient, in whom the anemia developed 19 years after the discovery of a calcified thymoma and 13 years after the appearance of the first signs of myasthenia. This led the authors to conduct a prospective study for the presence of intrinsic antifactor antibodies. A total of 81 patients (20 men and 61 women) with myasthenia were studied. The myasthenia had appeared after 35 years of age in 40 patients and 19 had a thymoma. The results of the study for the antibodies was positive in 3 women, as was the test of inhibition of leucocyte migration, but none of them had anemia, vitamin B12 malabsorption, achlorhydria, or gastric atrophy. The discovery of these immunological disorders raises the problem of their significance ; two hypotheses can be discussed : pre-Biermer state or immunological disturbance without pathogenetic significance. The problem can probably only be resolved by studying these antibody levels in a very much larger number of patients with myasthenia.