The reactions of the free radicals eaq- minus, OH and Br2- minus with haemoglobin-free erythrocyte ghost membranes have been studied by producing the radicals by pulse radiolysis and monitoring their reactions by optical spectroscopy. Hydrated electrons react rapidly with the membrane, but no attack at disulphide links was observed. Hydroxyl radical attack produced transient species absorbing weakly in the ultraviolet, which may arise from carbohydrate residues, such as N-acetyl neuraminic acid and N-acetyl glucosamine, on the membrane surface. No evidence was obtained for OH attack at ring-containing amino acid residues of the protein component. The Br2- minus radical, a more selective electrophile than OH, reacted only slowly with erythrocyte ghosts. Solubilization of the membranes with dodecylsulphate or digestion with alkali exposed protein containing tyrosine and tryptophan residues which reacted with Br2- minus. These results support other evidence for the absence of reactive protein at the membrane surface.