[On the proof of MN-differentiation from blood samples (author's transl)].

1. The results of MN testing are--so far as the factor N is concerned--especially in the case of older samples to be used only with caution. 2. The provision for a reliable result demands several good sera that have been previously used in testing and found to be satisfactory. 3. It is especially necessary to work with two different methods. The mixed agglutination method is no longer reliable in cases of months-old or very dryly stored samples.