Summary. An example of persistent mixed‐field polyagglutination of the Tn‐type is described, with particular reference to the value of plant seed agglutinins in the elucidation of polyagglutinable states. Extracts of the seeds of Dolichos biflorus, Bauhinia variegata and Wistaria sinensis strongly agglutinate Tn‐polyagglutinable cells. Inhibition studies indicate that N‐acetylgalactosamine may be an important determinant of Tn‐specificity. Positively charged polymers such as polybrene aggregate normal erythrocytes but not those appreciably deficient in sialic acid such as T‐ or Tn‐polyagglutinable cells. This observation forms the basis of a simple method of separating polyagglutinable from non‐agglutinating cells in a mixed‐field Tn‐polyagglutination. There are indications that Tn‐polyagglutinability, haemolytic anaemia, leucopenia and thrombocytopenia may constitute a distinct haematological syndrome.