A preliminary study has been made of the Righi‐Leduc effect in mercuric selenide (HgSe). The Righi‐Leduc magnetothermal effect is the thermal analog of the Hall effect wherein temperature plays the role of voltage and heat flow replaces electric current. The effect is particularly large in HgSe because of the coincidence of large electron mobilities (as high as 1.5 m2/v sec at 300°K) and low lattice thermal conductivity (about 0.02 w/°K cm at 300°K). Results are presented of measurements of the Righi‐Leduc coefficientSas a function of temperature, magnetic field strength, and electron concentration. Classically, for a one‐carrier material,S≅(&kgr;E/&kgr;)&mgr;, where &kgr;Eis the electronic, &kgr; is the total thermal conductivity, and &mgr; is the electron mobility. This expression is in qualitative accord with the experimental results. At room temperatureSranged between 0.27 and 0.34 m2/v sec for samples that had between 55×1017and 5.6×1017electrons/cm3.