Hydroponic culture and H¹⁴CO₃^- isotopic tracing were conducted to study on the distribution and transfer of HCO₃^- assimilates in Zn-inefficient cultivar IR26 and Zn-efficient cultivar IR8192-31-2 in relation to rice cultivar adaptation to Zn deficiency.The results showed that IR26 accumulated more HCO₃^- assimilates in the roots than IR8192-31-2.whereae,the latter is faster in root-to-shoot transfer of HCO₃^- assimilates.Zn application enhanced transfer of HCO₃^- assimilates from roots to shoots of Zn-inefficient rice.¹⁴C-activities were higher in all Zones of excised roots of IR26 roots than in that of IR8192-31-2,which implied that IR26 roots absorbed more H¹⁴CO₃^- than IR8192-31-2 roots.Moreover,transfer rate of H¹⁴CO₃^- assimilates from root tip to enlogation zone was higher for IR26 than for IR8192-31-2.It could he concluded that the difference in distribution and transfer of HCO₃^- assimilates were major mecha nisms responsible for Zn efficiency in lowland rice.