Abstract.Erythocytes from 3 Gerbich‐negative siblings readily converted to echinocytes when subjected to changing concentrations of sodium or lithium chloride. When erythrocyte membrane proteins were assayed by immunoblotting with human anti‐Ge 1,2, normal membranes were found to contain a reactive component of an approximate molecular weight of 33,000 daltons which was absent from the Gerbich‐negative individuals. PAS staining and mobility on SDS gels identified this component as glycophorin C. These observations indicate that glyocophorin C (β‐sialoglycoprotein) is a component of the Gerbich antigen and is involved in normal cell shape mai