1. Erythrocytic sodium-lithium (Na-Li) countertransport (CT) was measured in normotensive Maori and non-Maori by in vitro and in vivo methods to determine its relationship to erythrocytic hypernatraemia previously identified in Maori. 2. In vivo and in vitro CT rates were correlated within race and were similar between races. Countertransport rate was correlated with erythrocytic sodium concentration only in Maori. 3. The findings suggest the possibility of a genetically determined alteration in CT stoichiometry in Maori.