In the final set of experiments, the effect of o-vanillin was tested on RBC volume and K+ efflux. Following 60 min deoxygenation, RBCs from HbSS patients fell from 1.88 ± 0.01 to 1.74 ± 0.05 ml/g dcs in the absence of o-vanillin, and to 1.52 ± 0.01 in its presence. Notwithstanding its inhibitory effects on the defined K+ pathways, o-vanillin was therefore found to cause a reduction in RBC volume. K+ effluxwas also found to increase from 0.091 ± 0.012 h−1 to 0.192 ± 0.12 h−1.