The sodium–lead phase diagram has been determined up to 7·8 atom % lead by thermal and resistance methods. A eutectic occurs at 0·10 atom % lead and 97·32 °C. The partial molar enthalpy and entropy of solution of lead in liquid sodium is 7·07 kcal (29·6 kJ)/g atom and 5·52 cal (23·1 J)/°C/g atom respectively.