We therefore investigated the effects of o-vanillin on this pump. Results are shown in Fig. 6. For RBCs from both HbSS and HbSC patients, control Na+/K+ pumping activity gave an ouabain-sensitive K+ influx of about 4 mmol (l cells h)−, around 50% higher than usually observed in normal RBCs. In the presence of o-vanillin, inhibition of pump activity in RBCs from both genotypes was about 80% (Fig. 6).