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, which allows the use of agarose-bound ECL to isolate or fractionate mammalian glycoproteins. ECL is useful for isolating human natural killer (NK) cells using negative selection panning. These cells lack accessible carbohydrate structures required for binding ECL and, unlike other mononuclear cells, do not adhere to ECL-coated dishes. High recovery of viable NK cells is possible. Adherent cells can also be recovered by incubation in galactose or lactose. This fluorescein-labeled lectin features a ratio of fluorophores to lectin protein that provides optimal staining (excitation 495 nm, emission 515 nm). Supplied as a solution essentially free of unconjugated fluorophores, it is preserved with sodium azide. The recommended inhibiting/eluting sugar is 200 mM lactose.