following complete deoxygenation sickling was unaffected by the presence of o-vanillin (being 98±4%,mean± S.E.M., n=5, of control values in the absence of o-vanillin). It would therefore appear that o-vanillin can substantially inhibit both KCC and the Gardos channel without any inhibition of HbS polymerisation and sickling. Similar findingswere obtained using RBCs fromthe secondmain genotype of SCD patients, heterozygous HbSC individuals, with KCC and Gardos channel activities reduced to b20% their magnitude in the absence of o-vanillin (5 mM).