The interaction between normal or glycated haemoglobin and the cytoplasmic surface of human erythrocyte ghost membranes from normal and diabetic individuals was studied at low pH and low ionic strength. Haemoglobin binding to the membrane was monitored by quenching of a fluorescent probe, 12-(9-anthroyl) stearic acid, embedded in the membrane. The quenching occurs by energy transfer from the probe to the membrane-bound haemoglobin molecules. It was found that both glycated and non-glycated haemoglobin bind with higher affinity to membranes from diabetics than to control erythrocyte ghosts. The binding of glycated haemoglobin is significantly less than that of normal haemoglobin to red blood cell membranes from both normal and diabetic individuals.