Twelve of 35 members tested in a large ethnically-mixed South African family were found to have both haemoglobin M type Hyde Park and persistent polyagglutinable red blood cells. The characteristics of the polyagglutination have not been recorded previously. The cells of affected family members were not agglutinated by Arachis hypogea, Dolichos biflorus or Salvia sclarea, but were agglutinated weakly by Salvia horminum and BSII (GSII) and reacted strongly with Glycine soja and Sophora japonica lectins. BSI (GSI) lectin agglutinated the group A but not the group O cells. The N and MN cells were agglutinated more strongly than normal by Vicia graminea, other anti-N lectins and human anti-N but the M and MN cells reacted as expected with human anti-M. The name 'Hyde Park' is provisionally suggested for this type of polyagglutination, although it appears unlikely that the evidently complete association between the polyagglutination and the variant haemoglobin is the result of a single genetic mutation. More likely, the connection has a post-genetic origin, perhaps showing that bonds, possibly affected adversely by precocious senescence, normally occur between the haemoglobin and alpha-sialoglycoprotein molecules in red blood cells.