Erythrina cristagalli lectin (ECL, ECA) binds a carbohydrate structure frequently found in mammalian membrane and serum glycoproteins. Sialic acid substitution on this structure prevents binding, and this specificity offers an opportunity to use ECL to isolate or fractionate glycoproteins. ECL has been useful for the isolation of human natural killer (NK) cells using a negative selection panning technique (protocol available). Human NK cells lack accessible carbohydrate structures required for binding ECL and, unlike other mononuclear cells, do not adhere to ECL-coated culture dishes. Since this procedure involves a negative selection panning technique, a high recovery of viable NK cells can be obtained. The adherent cells can also be recovered by incubation in galactose or lactose.