We have measured hydrogen partition coefficients between nominally anhydrous minerals (olivine, pyroxenes) and basaltic melts in 13 hydrous melting experiments performed at upper mantle P-T conditions (1--2 GPa and 1230--1380¿C). Resulting liquids have 3.1--6.4 wt.% H2O and average mineral/melt partition coefficients as follows: DHol/melt = 0.0017 ¿ 0.0005 (n = 9), DHopx/melt = 0.019 ¿ 0.004 (n = 8), and DHcpx/melt = 0.023 ¿ 0.005 (n = 2). Mineral/mineral partition coefficients are DHol/opx = 0.11 ¿ 0.01 (n = 4), DHol/cpx = 0.08 ¿ 0.01 (n = 2) and DHcpx/opx = 1.4 ¿ 0.3 (n = 1). These measurements confirm that water behaves similarly to Ce during mantle melting (DHperidotite/melt is ~0.009). For mantle water concentrations of 50--200 ppm, the onset of melting is 5--20 km deeper than the dry solidus, less than previous estimates.