We report experimentally determined 1atm olivine/melt D Na partitioning data for low f O2 , a variety of melt compositions and a temperature range of 1325–1522°C. We demonstrated that high-current electron microprobe analyses (EPMA, I=500nA, 600s on the peak) allow quantitative determination of Na 2 O in olivine down to ∼10μg/g. The mean olivine/melt D Na from 12 experimental runs is 0.0031±0.0007 (1σ). This is the recommended value for low pressures and a wide range of natural compositions.This result is applied to the problem of the origin of alkalis in chondrules and the formation of chondritic refractory forsterite grains. The data on Semarkona (LL3.0) chondrules show that Na 2 O is primordial and was present during olivine crystallization. For refractory forsterite grains from Murchison (CM2), we demonstrate that high CaO contents are not a result of equilibration with Na 2 O-rich melts, but require high activities of CaO during their formation.