Blood samples from two patients with autoimmune haemolytic anaemia, whose autoantibodies failed to agglutinate certain examples of red cells that lack Gerbich blood group antigens, were studied using immunochemical analyses. One of these autoantibodies differed from all other anti-Ge in that it showed a unique beta sialoglycoprotein (SGP) specificity. It reacted with normal beta but not with the abnormal beta-related SGPs associated with Gerbich-negative red cells of the Gerbich and Yus types. Red cells from this patient had an alteration of beta SGP, while the alpha, gamma and delta SGPs appeared to be normal. The autoantibody from the other patient did not show this unique characteristic. Its immunochemical specificity was similar to alloanti-Ge3 in that it reacted with both beta and gamma SGPs from normal red cell membranes and with the abnormal beta-related SGPs found in red cell membranes from individuals with Gerbich-negative red cells of the Yus type. Red cells from this patient could not be analysed because she had recently received a massive transfusion of red cells.