1The uptake of 86rubidium by erythrocytes from mothers and babies has been used as a model system to investigate possible differences in sensitivity to digoxin in the very young. 2 While total 86#rubidium uptake was not significantly different between mothers and babies, the digoxin-sensitive proportion was higher in neonatal erythrocytes. Neonatal cells were less sensitive to digoxin, denionstrated by the requirement for a larger amount of digoxin to inhibit 816rubidium uptake and this was accompanied by an increase in numbers of specific erythrocyte binding sites for digoxin.3 These results provide further evidence in support of the hypothesis of decreased sensitivity to digoxin in the very young.