Portions of the NaOH-NaH phase diagram were studied by means of differential thermal analysis. Under certain conditions NaH will either react with NaOH according to the equation NaH + NaOH in equilibrium Na/sub 2/O + H/ sub 2/ or thermally dissociate according to the equation NaH in equilibrium Na + 1/2 H/sub 2/. Both of these reactions are suppressed by a high H/sub 2/ pressure; and NaH neither reacts nor dissociates to an extent sufficient to affect the results reported. This was evidenced by the fact that changing the H/ sub 2/ pressure above the system in the range indicated did not change, within the limit of error of the experiments ( approximately plus or minus 5 deg ), the temperature at which a phase change was started or completed. Therefore the concentrations of Na and Na/sub 2/O present in the samples must have been small in all cases. Under a high H/sub 2/ pressure, therefore, the system may be considered as essentiallybinary, consisting of NaOH and NaH. (auth)