In three children with haemolytic uraemic syndrome (HUS), evidence of red cell polyagglutinability due to Thomsen Friedenreich antigen (T-antigen) exposure was demonstrated. This was suspected after difficulties in ABO typing and was confirmed using specific antisera. Further supportive evidence included elevation of plasma sialic acid, alteration in red cell surface charge and evidence of T-antigen exposure in the renal biopsy specimen of one patient. Although involvement of this antigen in the pathogenesis of HUS has been associated with a high mortality, all three children have made a complete recovery. With early recognition and subsequent avoidance of plasma products, prognosis of this condition may be improved.