Two-dimensional, time-dependent calculations show that the thermal and flow structures can be influenced by the lower-mantle thermal-chemical instabilities. The style of the core-mantle boundary (CMB) deformation in thermal-chemical convection is different from that obtained in thermal convection. The amplitude of CMB hills is reduced greatly from the depth-dependence of thermal expansivity, found in recent high-pressure experiments. ¿ American Geophysical Union 1989